A forest ranger finds a badly burned body. It's Ellie Simms, a missing Marine cryptologist. Callen decides to investigate and reluctantly takes along Eric when he volunteers. Kensi and Deeks talk to Simms's widower Calvin, who said she didn't fit into civilian life and was suffering from PTSD. Ellie was working for the DEA decrypting messages. Ellie was tortured before she was killed by professionals. Ellie had discovered texts from ISIS in Syria to L.A. Her supervisor, Michael Baird, was skeptical about her findings and thought she made them up. He said the texts had disappeared when he went to review them. Baird takes off afterward, and Sam and Callen follow him. He goes to his home shed, which blows up. Sam and Callen visit Skip Mattson, suspected of stealing the explosives used in the bombing, and he is killed in a firefight with them. Mattson, an ISIS sympathesizer, was in contact with two sailors on board the aircraft carrier USS Allegiance. Sam and Callen fly out to help NCIS Special Agent Afloat Brian Lee investigate aboard the carrier. Baird had an alibi for the time of Ellie's death. Eric sends Nell to check on her mother, who has regressed. Deeks doesn't buy that ISIS is after a military target. He and Kensi decide it's more likely an espionage operation. Eric figures out Volkoff had called Baird's wife Olivia from Cuba before he died. So it's probably a Russian intelligence operation. Sam and Callen meet Captain Harmon Rabb. Lee is missing and thought to be a man overboard. Michael Baird was born a Russian citizen, changing his last name to hers when they married. Olivia Baird's office is vacant. The search finds the body of Lee, who had been stabbed six times. Someone had cleaned up the crime scene onboard.