It's been almost a year since Orange Is The New Black's first season dropped on Netflix, and since then you've probably True Detectived and Girlsed and BreakingBadded all the salient plot information out of your head, so let's get back up to speed.
Release dates and season 2 rumours here, season 1 episode-by-episode below, and the TL;DR at the end.
S01E01 Piper leaves her apartment and Mad Men box sets behind and enters Litchfield. Clashes with prison matriarch Red. Discovers her ex-lover and accomplice Alex is in the same prison.
S01E02 Piper is starved by the kitchen staff, but eventually wins Red over by making her a lotion for her back. 'Crazy Eyes' makes crazy eyes at her.
S01E03 Mostly deals with Sophia Burset's gender reassignment back story. Piper resists Crazy Eyes advances and moves into Miss Claudette's cube.
S01E04 Piper accidentally steals a screwdriver from the prison workshop, but Claudette helps her evade the blame. Piper starts reviewing appealing letters for others.
S01E05 Larry discovers that Alex named Piper to the police but decides to keep it from her. She misses an important business call Polly arranged in order to chase a chicken.
S01E06 Unaware Alex betrayed her, Piper starts to look at her former lover fondly. She also confronts her mother and gets elected to the prison council, while Daya and prison officer Bennett get closer.
S01E07 Alex steps in to help Piper during a dispute with Pennsatucky. Mendez pressures Red to smuggle drugs into the prison.
S01E08 Larry's article about life with a girlfriend in prison is published and Piper isn't happy. Polly gives birth. Dayanara gets pregnant. Taystee is granted parole.
S01E09 Mendez and Red continue to clash. Alex's back story is fleshed out with her estranged relationship with her father and beginnings in the drug trade. She and Piper end up having sex, and it is implied that Healy calls Larry to tell him.
S01E10 Bennett frets over his illicit relationship with Dayanara. Mendez manipulates Miller into selling drugs, and when she overdoses he covers her death up as suicide by hanging.
S01E11 Miller's death is covered up, but Nichols and Red vow to bring him down. Larry gives a radio interview that doesn't paint Litchfield inmates in a good light, which makes things hard for Piper. Piper tells Larry that she loves Alex, who, deeply angered, informs her that Alex ratted on her. "How does it feel to be in love with the woman who ruined our lives?" he asks.
S01E12 Alex tells Piper that she only ratted on her as revenge after their break up, and asks her to choose between nesting with Larry or living a more dangerous life with her.
S01E13 Piper tells Alex that she is choosing Larry, but when Larry visits Alex to warn her to keep away from his fiance, she tells him that it was Piper that rekindled their sexual relationship and Larry breaks up with Piper. Piper comes crawling back to Alex, who will not take her. Now completely alone, Piper slides into depression and when Pennsatucky provokes her, coming at her with a shiv, Piper sees red and beats her to a bloody pulp.
TL;DR Piper enters prison a rabbit in the headlights, but slowly grows stronger. Her ex Alex being in the same prison puts a strain on her relationship with Larry and she is eventually forced to choose who she wants to be with. She goes with Larry, but he discovers about her betrayal with Alex and ends things, leaving Piper all alone. The season ends with her in a bloody fight with Pennsatucky, and facing a long time in solitary in season 2...