Tuvok’s recent unexplained bout of flashbacks appears to coincide with Voyager’s passing of a nearby nebula rich in sirillium. Unfortunatley, flashbacks are known to destroy brain tissue in Vulcans, leading to death. While there is nothing the doctor can do, a mind meld can help Tuvok to find where the flashback is coming from and stop it. Janeway agrees to help Tuvok, and their meld takes them back in time 80 years when Tuvok had served aboard the USS Excelsior, then being captained by Hikaru Sulu.