Voyager is being chased by three alien warships. Outnumbered and outgunned, Voyager takes refuge in a gaseous nebula cloud. Unable to scan them, the ships don't enter the nebula. Janeway orders Kim to help B'Elanna with some repairs, and as he enters the turbolift, he suddenly finds himself on a Borg ship. He and another Borg are at a medical table, busy assimilating a screaming woman. The other Borg looks up at him, and telepathically addresses him as Seven of Nine. Then, just as suddenly, he is back in the turbolift. He is very confused. Whatever happened to him was very real, and it seemed to be a scene from Seven's life. When he asks Seven about it, though, she can't remember the woman. This is odd, because she should be able to remember things she did in the collective. She offers to investigate. Meanwhile, in Engineering, Torres is working on a conduit when she suddenly finds herself on a strange planet. As she looks around, she finds she is standing next to a young Vulcan woman, and a Vulcan priest is chanting something in Vulcan. After a moment of total confusion, she is back in Engineering. This continues with several of the crew. Neelix finds himself at Starfleet Academy in a lecture hall. The cadet next to him turns and says "you better pay attention, Harry." Chakotay finds himself walking a dog on Earth - the same dog, he realizes, in one of Janeway's photos. Seven suddenly finds herself in a penal colony in New Zeland. It is now evident that many of the crew members are experiencing memories of other crew members. But, the disturbing part is - those memories seem to be erased from the host! Tuvok can't recall his wedding day, Janeway can't remember what her dog looked like, etc. Janeway presumes the nebula is the cause, but a quick trip to the edge of the nebula brings on a few photon torpedos - the alien ships are still lying in wait. For the moment, they're stranded in the nebula. This memory changing continues, and soon some of the crew can't seem to remember ho to do their jobs. B'Elanna seems lost in Engineering, Tom forgets how to work his CONN console, Tuvok accidentally fires the phasers, etc. It seems almost everyone is losing some or most of their memories. Soon, the cloud begins affecting the ship as well. Environmental systems go off line, impulse engines fail, power systems fluctuate, the computer malfunctions, etc. It is obvious that they must leave the nebula. But, what if their memories are still lost? They were taking a pounding from the aliens with all their faculties in place - what will happen if they can't remember what to do? Since they can't leave, they start concentrating on the nebula and how it is affecting them. But, to everyone's surprise, they have literally changed roles as their memories have changed. Neelix is now the scientific expert. Seven seems at home at the weapons console. Chakotay takes over the CONN. In these new roles, they find the cause… Tiny particles in the nebula are penetrating Voyager's shields, and as they pass through the ship, they are taking memories with them - not only human memories, but the computer's bio-neural memories as well. Suddenly, they are fired on. The aliens have finally entered the nebula. In their new roles, they try to maneuver and fight. However, to their surprise, the consoles don't work properly. CONN controls weapons. Engineering controls the CONN, etc. When it looks like destruction is eminent, Neelix finds a way to track and retrace the paths of the particles, and uses a modified tractor beam to move the nebula's particles and place each memory back into the original host. With their memories returned and the ship working properly, they manage to hold off the aliens just long enough to escape the nebula and warp away to safety…
Lisa's comments: She felt this was just another "medical mystery."