Stranded in the year 2000 after a botched experiment, depressed and dysfunctional physicist Sarah has the opportunity to offer her own younger self some much-needed guidance, and help her to make better life choices than she did the first time round. The problem is, 14-year-old Sarah is a whole-ass handful; a volatile troublemaker, hellbent on using her time-travelling older self for profit and power.
Big Sarah experiences withdrawals from her antidepressants, while Little Sarah torments her, both to amuse herself and to gather as much juicy data as she can. Faced with the reality of Little Sarah's chaotic cruelty, Big Sarah makes the unexpected decision to disclose something massive about their future.
Finally in possession of future knowledge worth having, Little Sarah flexes her manipulation skills, until reality smacks her in the face. Big Sarah is ambushed into a "family dinner" and learns something about her parents she wasn't expecting.
Little Sarah experiences her first girl crush, and is TOTALLY NORMAL ABOUT IT. Meanwhile, Big Sarah blows off some steam with a hot bartender, leaving her with a brand-new existential crisis and her pants on backwards, before discovering a profound betrayal by Little Sarah.
Roped into babysitting Little Sarah, Big Sarah must survive an entire weekend trapped in the house with the megalomaniacal psycho who has been using her for information and profit. Finally fed up, she hatches an escape plan. Meanwhile, with the parents away, Little Sarah throws her best party to date.
Faced with the threat of Big Sarah leaving - and being obliterated in a new timeline - Little Sarah finally tries to be a better person, which goes even worse than you'd expect. Big Sarah, finally honest with herself, makes a selfish decision.