When you watch NCIS Season 15 Episode 23 online, Gibbs is attending a memorial service for an old friend, Navy Captain Phil Brooks, who was lost at sea while sailing in bad weather in his personal boat. After Brooks' wife Marcy asks Gibbs to take Phil's woodworking tools, Gibbs discovers a hidden door in the workshop. The door leads to a secret fallout shelter underground, where, much to Gibbs' shock, he discovers Phil Brooks, alive and well. Brooks had been waiting for Gibbs to turn up and reveals that someone had actually attempted to murder him by shooting at his boat. In desperation, Brooks dove for it and successfully swam to shore. Unfortunately, he never got in touch with Gibbs because he left the message of his survival with Reeves, who died shortly thereafter. Now knowing that Brooks is alive and someone tried to murder him, Gibbs decides that it's time for him and his team to investigate the incident. CGIS isn't thrilled about handing over the case, but it doesn't take long for them to find evidence supporting Brooks' story. Will the team be able to learn who is trying to kill him and why? Find out what happens when you watch NCIS Season 15 Episode 23 online!