Jake and Amy are excited to go on their first real vacation together, but Amy's perfectly planned cruise ship itinerary is thwarted when they discover an old adversary is on board with them. Meanwhile, Gina and Terry help Captain Holt survive a visit from his sister, Debbie, and Charles and Rosa vie for the same apartment.

The Nine-Nine host the detectives from the Nine-Eight, their neighboring precinct, reuniting Jake with his old partner. Charles is immediately jealous and tries to reclaim his best friend status with Jake. Meanwhile, the rest of the precinct tries to be welcoming to the Nine-Eight, but it doesn't go as well as they had planned.