Dale Harding, a retired Marine gunnery sergeant, shoots himself. Jane Tennant and Jesse Boone from NCIS: Hawaii are in town for Harding's retirement party. But Director Vance breaks the news to everyone that Harding was found dead in his apartment, reportedly by suicide. Everyone from both teams heads out to investigate his death. But they're beaten to the scene by Sam and Callen from NCIS: Los Angeles. Suicide didn't make sense for Harding, known to his students as "The Cockroach." Harding's cell phone is missing. Harding's computer was used after his time of death. Harding left the message "Extra homework" on his computer. Kasie discovers that Harding deleted sensitive defense files before his suicide. Harding had hacked the files. Sam, Callen, and Torres search Harding's office. Harding's fellow instructor Greta Ford says he planned to meet a friend in Hawaii. He switched his travel plans to go there instead of Cabo. Sam and Callen arrest McGee, who DOD thinks is the hacker. Harding stole McGee's login information when they had lunch the previous week. Kasie finds a floppy disc with the heading "Extra homework." Inside is the message "The answer is in the files." Harding had hid the files in the fireplace of Gibbs' cabin. Torres and Jessica are shot at when they go to the cabin. The wounded shooter escapes on a motorbike. The files are gone. Torres and Jessica find Harding's phone in the shooter's bloody jacket. Harding's last call was from the wanted criminal Simon Williams. Harding had cut Williams from the FLETC program. A sheriff's squadcar is missing. Torres and McGee find the shooter in a barn and the younger man claims to be Simon Williams before dying. He burned the files. Palmer and Tennant go missing, failing to show for dinner with Torres and Jessica. They've been abducted.