Star Trek: Voyager S01 E11 Heroes and Demons

"Charting the new frontier"

Stardate: 48693.2. Harry Kim disappears from the holodeck during his holo-novel, "Beowulf." According to the characters, he died at the hands of a mystical beast known as "Grendel". When Chakotay and Tuvok also disappear, the Doctor is transferred to the holodeck to investigate.