A bomb explodes in the bed of the pickup truck of a Marine former second lieutenant; he runs; FBI agents bust him; Granger wants to find out why the team did not previously know about a terrorist plot in the LA area; they figure it out.

A joint task force (involving the CIA, FBI, and NCIS) raid a meeting in a house in an attempt to capture members of the Molina drug cartel and the Al Qaeda; however, they walk into an ambush; the new SecNav, suspecting a mole or other leak, directs the Callen team to investigate and correct; at the boatshed Kensi and Deeks interview four participants in the raid; Eric determines that the problem is not a mole but rather a hacker, which, Hetty says, is even worse; on the cellphones of two agents Eric discovers the hacker's malware, which allowed the hacker to intercept all calls, both incoming and outgoing; in an alley the foursome grab the hacker (Cindy, a 15-year-old girl) and her laptop computer; G suddenly becomes a substitute teacher, then he finds the track coach wearing a belt as a necklace; Eric finds a link and the man responsible; the gang figure out everything; with Cindy's help the team grab the bad guy who misused Cindy and her activities.