There Were Never Such Devoted Sisters
Rollins (Kelli Giddish) comes home to the sound of her sister Kim (Lindsay Pulsipher) being assaulted by her ex-boyfriend Jeff (Theis Weckesser). Kim yells that Jeff has a gun -- indeed, he is reaching for it -- and Rollins fatally shoots him.
Kim, having had enough of Jeff's physical abuse, secretly took out a life insurance policy on him, naming herself and Rollins as beneficiaries. She then returns to New York; lies to Rollins about being pregnant to gain her sympathy; baits Jeff to come looking for her with strategic Foursquare check-ins; manipulates Rollins into getting an order of protection against Jeff; calls Jeff to come over; and pretty much choreographs the whole scene so that Jeff ends up dead. Unfortunately, the insurer won't pay out on the policy if the decedent was killed in the course of committing a felony, so she tries to retcon the situation so that it appears as though Jeff's death was an accident, and then later changes tack again and plants seeds with IAB to the effect that Rollins has had it in for Jeff since they met, and did not shoot him in self-defense, resulting in Rollins's arrest for murder. Kim's not a great sister.
"Our pizza delivery rapist struck again"; "He wasn't really raping me, you know? He tried, but he couldn't...you know"; "It's to make sure that the department is covered if I eat my gun."
Rollins sees her sister despite express orders from everyone that she shouldn't; IAB enforcer/recurring villain Tucker (Robert John Burke) clearly tries to game the investigation to make Rollins look guilty, right up until the moment Amaro (Danny Pino) delivers audio, probably not entirely legally recorded on his phone, of Kim admitting to her plot.
Well...Rollins, what with her getting wrongly arrested for murder and everything.
To Be Determined: when Tucker goes to Kim's hotel to arrest her, she's disappeared. (For good measure, she's also emptied out Rollins's entire apartment, including the fridge.)
"Captain, if I'm shooting, I'm emptying the whole gat," says Fin (Ice-T) in the course of a training exercise, possibly foreshadowing a situation at some point this season in which that happens. Also, Rollins reveals that although the bookies she'd used during the worst of her gambling addiction are both now in prison, she still technically owes them $20,000.