Jake and Amy embark on a romantic cruise, only to find an old adversary aboard. Holt braces for a visit from his melodramatic sister.
An illness leaves Jake and Holt quarantined and delusional as they try to solve a cold case. Terry discovers running the precinct is messy work.
Boyle tries to recover some sensitive cargo held hostage by his ruthless ex-wife. Amy injures Terry at the worst possible moment.
A last-minute Christmas shopping trip lands Jake, Gina and Charles in the middle of a "Die Hard"-like hostage crisis.
Tensions flare as Jake and Rosa work a case with two peculiar Swedish cops. Neil deGrasse Tyson drops by to help Gina prepare for a big test.