Series 1 and 2
In "Tony" Effy is seen one morning briefly walking home at the beginning of the episode, apparently from partying the night before. Her brother Tony distracts her father so that she can sneak back into the house, a routine they are both clearly familiar with.
In "Effy", Tony is forced to care about someone other than himself for once when Effy -- one of the only people he cares about -- disappears. When Effy and Tony are having a meal with their parents, they are both grinning at each other whilst their father tells them a story they've heard many times before. Later on, we see Effy sneak out the house and Tony, seeing her go, climbs into her bed wearing her red and black striped socks and hiding under the cover, only socks exposed, so that when their parents come in, they think they see Effy fast asleep and leave her be. We see Effy, and her rather talkative acquaintance, meet up with some boys who know Effy. One of the boys is called Spencer (played by Tom Payne), and him and Effy end up kissing and taking pills together. Effy ends up being taken to a sports hall where she takes drugs through a needle, speaking her first line in the whole series before passing out.
Josh Stock had been the one to orchestrate the event, so he could get revenge on Tony. Having Spencer break Tony's phone, Josh promises that she will only get to a hospital for her apparent OD if Tony has sex with his unconscious sister, relating to Tony's scheming last week. Eventually, Tony is in tears in just his boxers, after Josh strips him down, while Spencer tries to intervene, begging, and Josh lets him take Effy to hospital where her parents, Tony and Sid Jenkins are told she has taken clean pharmaceuticals and will be fine.
In the series finale, we learn her parents have moved her to the private school which Josh and Abigail Stock attend in the aftermath of her drug episode. More layers to her character appear as she derides Tony verbally as a wanker for his treatment of ex-girlfriend Michelle, who had come to her previously in an attempt to understand Tony. She witnesses as Tony is hit by a bus, and screams in horror, crying silently as the finale takes place.
In the second series, we learn that Effy has now begun to speak openly, at least amongst her family and presumably among others as well. She also continues to party, as seen in the first episode of the second series, despite the events of "Effy" where both she and Tony were put through a traumatic experience.
In the sixth episode "Tony" it becomes clear that she is looking after Tony since his accident, where she is seen comforting him from his nightmares by reading him Greek myths. She also speaks to Michelle and Sid, but is fairly unfriendly with both of them, possibly in response to Michelle and Sid's new found relationship, or likely simply out of loyalty to her brother.
In "Effy", episode 7 of the series, Effy is the central character. She is seen walking around the house smoking a cigarette before school, where the house is clearly in disarray. Her father is in France for business, and her mother is depressed from Tony's accident, where she has seemingly taken to abusing pills and laying in bed all day. Effy on the other hand has taken on the role of a parental figure somewhat, where she is seen washing and drying her and Tony's clothes (albeit ineptly), and watching after her mother.
At school Effy's art teacher appoints Effy to the task of helping new girl Pandora, and explains that she must do well on her GCSE Art coursework or else she'll be expelled. Although Effy clearly objects to the former, she allows Pandora to follow her around, and even takes her home with her. Back at home Tony receives a parcel from Michelle, which is actually the watch (now broken) he gave her for her birthday, prompting him to become further frustrated with Sid. Sid explains to Effy his problems, in which she agrees that in exchange for doing her GCSE Art coursework, she promises to sort out Sid's struggling social enterprises; specifically concerning his love for the estranged Cassie.
Effy, with Pandora in tow, goes to pick up drugs at Cassie's where she inquires about her relationship with Sid, but otherwise doesn't probe the subject. She is seen taking drugs to a club, where she sells them and is also seen by Tony selling Michelle's watch, prompting him to be angered with her. It is revealed later that Effy didn't sell it however, but instead had it repaired and sent back to Michelle with the word "forever" engraved in it, softening Michelle enough to speak to Tony again. As for Sid, Effy sends an acquaintance of hers called Jake to Cassie's -- knowing the chances that they would sleep together -- and takes a series of photos through the window. She scatters the photos around Sid's sleeping form, prompting him to finally confront Cassie, where the two subsequently make up.
At school Effy doesn't use Sid's artwork he created for her, but explains to her teacher that her GCSE Art coursework is conceptual, in which she used an array of emotions -- referring to her recent experiences helping others mend their relationships. At the end of the episode Effy's father arrives home to a clean house, and his wife in a elegant state, all presumably done by Effy.
In the finale of the second series, "Everyone", Effy is seen in the final shot before the credits, smirking at the camera and smiling while lying under Tony's duvet cover, foreshadowing her presence as the lead character in the third series.
 Series 3
Effy's father drives her to her first day at Roundview College, but gets into a car accident after driving over a bike in the road. Effy waits silently in the car as her father engages in an argument with an elderly bystander, where she catches the eye of best friends Freddie, Cook and JJ. At college Effy waits outside with her best friend Pandora, where she observes twins Emily and Katie come into school with mild interest. During a welcoming ceremony in the auditorium/gym, Effy and Freddie make eye contact again, but it is also apparent that Freddie's friend JJ is also interested in Effy when he mistakes her looks directed to Freddie for himself. When Freddie attempts to engage in conversation with Effy at her locker, explaining that he'd like to get to know her, she warns him that his best friends Cook and JJ want the same, which will likely make things "complicated". She then gives him a list of all the things they're not supposed to do in school, and whoever -- Freddie, Cook, or JJ -- completes it first before the day's end, she'll grant an opportunity to "get to know".
Outside of Effy's class she and Pandora are formally introduced to the twins Katie and Emily from before, where Katie makes a bad impression on Effy. In class, after the teacher asks students to introduce themselves and share a single unique fact, Effy reveals that she suspects her mother is having an affair. At Freddie's turn, he reveals he met a beautiful girl, referring directly to Effy. By the end of the day, Cook is the only one to have completed everything on the list Effy had given them earlier, with the exception of sex and drugs in school. Effy excuses herself to go the nurse's office, prompting Cook to follow, where they light up spliff and the two have sex.
In "Cook", the second episode of the series, Effy and best friend Pandora, as well as her new acquaintances from school Katie, Emily, and Naomi celebrate Cook's birthday party at a pub, where Cook's best friends Freddie and JJ are also present. Later on they manage to get into a posh party, where Effy goes into the bathroom and snorts drugs, but eventually they flee when a fight breaks out. When Cook proposes sex with Effy, she rejects him. In the following episode, "Thomas", Effy's suspicions from the first episode are confirmed when she catches her mother post-coitus with her father's boss, although unlike the first episode, Effy is visibly distraught at facing the truth of her mother's affair. She also helps new friend to the group Thomas sell drugs so that he may pay money off to gangster Johnny White. At the end of the episode its suggested that she and Cook have sex again.
In "Pandora" Effy's parents argue after her father discovers her mum is having an affair. Effy and Pandora witness the scene, upsetting Effy so much that she runs away. Later on they go to Pandora's house in which she is holding a "girls only" pajama party. Although Pandora makes it clear that drinking, drugs, and boys will not be tolerated, Effy both allows and encourages Katie to mix powdered MDMA in the brownies during preparation. Effy and Pandora's unknowing mum are the first to get trashed, prompting the distraught Pandora to lock herself in the bathroom for the rest of the night. Effy becomes upset and frustrated with herself when she realises she has upset Pandora, but otherwise continues to party (which has grown since Katie's boyfriend has brought friends). She has sex with Cook again, and afterward is confronted by Freddie for leaving JJ alone, prompting the disconcerted Effy to leave the party. The next morning Effy and her mother Anthea share a moment in the kitchen, in which the two are now alone since her father left. She then goes to Pandora's house to (presumably) apologise, only to catch Cook flirtatiously saying goodbye to Pandora, before she kisses him and sees him off. Effy confronts Pandora, to which Pandora finds the courage to tell Effy that she knows nothing about her or her family, explaining that Effy doesn't put enough effort into their friendship. Effy agrees, and leaves.
In "Freddie", Effy arrives in Freddie's garden and asks to be allowed into his shed. Inside, the two share a spliff, but are quickly joined by the arrival of Cook and JJ. When Cook invites Effy to leave to have sex with him, she sarcastically rebuffs him, causing him to angrily insist that she leave. Afterward, as Freddie returns a bracelet to her, he suggests that they would be "good together". Effy denies this by claiming she would break his heart. Later in the episode, Freddie seeks out Effy at the water-park, where she is escaping from her turbulent home situation. The two share a passionate kiss mid-water, where Freddie tells her how he feels about her. Nevertheless, by the end of the episode Effy has returned to Cook, and she and Cook watch from her bedroom window as Freddie watches from below.
In "Naomi", although there is apparent tension between Effy and Freddie, she and Pandora seem to be on better terms with one another. Effy observes Cook flirt in class, aware that he has sex with others, to which she has no objections. At the end of the episode she is seen celebrating Cook's win as class president. In the next episode, "JJ", JJ finds the courage to go to Effy's home and confront her for severing his, Cook, and Freddie's friendship. Although he politely pleas her to stop, she apologetically cannot guarantee him that she will. JJ also admits that he loves her, and Effy expresses sentiment that she would like to be his friend. Later on outside of a club, Naomi and Effy share a brief moment where Naomi seems troubled by her own sexuality, but Effy doesn't judge her. In turn Naomi cleverly points out that Effy is in love with Freddie, in which Effy feebly denies. Effy is also apprehensive when Freddie and Katie become open about their new found relationship.
In "Effy", it is apparent that Effy has gone 'dead inside' -- even when having sex with Cook she seems both physically and emotionally unfeeling. Downstairs Effy tells her mother she and Cook broke up (unbeknownst to Cook), much to her mother's apparent disinterest, who is busy dealing with her own emotional turmoil with Effy's estranged father. When Effy decides to go to Freddie's house to confront him with her feelings, she finds instead Freddie and Katie making out in his shed, who are now an item. Katie asks Effy to go on a camping trip (since she can drive) with them to a place called "Gobblers End" in which everyone is invited minus Cook, who Katie dislikes. Freddie suggests Effy come, much to Effy's surprise. When Freddie asks her why she came to his house in the first place however, Effy becomes discouraged, and leaves. Outside she becomes physically ill and pukes on her shoes, to which she walks home barefoot.
Effy borrows her mother's car and drives the group -- Freddie, JJ, Katie, Pandora, Thomas, Naomi, and Emily -- to Gobblers End. However the mood darkens significantly when at a petrol station asking for directions, a group of poachers spook them and even go as far as to wave their guns in Effy's face while on the road. At the campsite Effy wanders off by herself where she happens to discover some mushrooms. When Effy returns to the campsite, she attempts to comfort Pandora who seems gloomy -- but when Pandora doesn't open up -- Effy shows her the mushrooms in attempt to cheer her up instead. The group are thrilled about the mushrooms, except Katie.
Effy manages to have fun while happily high on the effects of the mushrooms and ends up holding Freddie's hand as they sleep. Katie however spots this and tells Effy she looks like a "desperate whore". Upon awakening, Effy goes to get her bag, only to realise all the bags are missing. Everyone becomes frightened, and when someone approaches their camp shouting and moving manically, Effy strikes the masked person and they both momentarily black out. Realising its Cook trying to scare them, everyone becomes angry and tells him to "fuck off", to which he retaliates by revealing their secrets, including Effy's: that she doesn't want (Cook) anymore, suggesting she loves Freddie. Effy and Freddie share a look, and Katie leaves. When Cook reveals that he and Pandora have continued sleeping together (Effy thought it was only once) Effy begins trembling. Freddie attempts to calm her, but she takes off through the woods.
In the woods Effy bumps into Katie. Katie takes advantage of Effy's crazed state, and messes with her head (such as telling the paranoid Effy she has bugs in her hair). Katie begins crying and begs Effy not to take Freddie from her, but when Effy tries to hug and comfort her, Katie angrily pushes Effy to the ground and grinds her face into the dirt as Effy attempts to gasp for air. Effy is rolled onto her back with Katie on top, and Katie pulls her hair, slaps her, and spits in her face -- all the while telling Effy not to "fuck" with her or "take" what "belongs" to her. When Katie begins choking Effy, who is freaking out, Effy reaches over for a rock and hits Katie in the head. The rock has blood on it when she sets it down, and Katie isn't moving.
Effy goes back to the camp and sits by Freddie's sleeping form. He awakens with his fist clenched and readied, but realises its Effy and stops himself before he hits. Effy dares him to hit her, telling him she wants to "feel something", but Freddie kisses her instead. The two have sex. The next morning Katie is missing, and although Effy remembers what happened, cannot bring herself to tell Freddie. After an unsuccessful search for Katie, they pack up and Effy calls an ambulance to come look for her. At home her mum Anthea realises something is wrong, and manages to put her problems aside to comfort Effy, who breaks down and cries as her mother washes her up. Effy tries to call her friends, but no one answers. Finally Freddie calls her and tells her Katie was found in the woods, but is unconscious and needs nine stitches.
By the time Effy arrives at the hospital, Katie has already awakened and told Freddie Effy hit her. After unsuccessfully explaining herself to Freddie, Emily, or Pandora, Effy blacks out and is eventually awaken by Cook, who is driving her somewhere. Neither of them know where they are heading, but they aren't seen in the following episode.