Things get personal for Danny when his former partner is murdered. His friend was being investigated by Internal Affairs, which make matters worse.
The team must deal with pirates who've taken a pleasure cruise full of spring breakers for ransom, as well as their worried parents.
When agent Lance Hamilton's partner is killed, Sam dons his previous undercover persona of "Switch" to find the culprit; Kensi, Deeks, Roundtree and Kilbride work to catch an aerospace engineer who stole classified Navy schematics.
The team hunts for a person who jeopardised a classified vaccine project, and Deeks must deal with his emotions as he returns to the field.
The team learns that Nate Getz is working with an infamous crime leader when he fails to check in during an undercover operation.