During Kate and Sawyer's escape from The Others, Alex met up with them, asking them to help her find Karl, who she said was her boyfriend. At this point, Sawyer realized that Karl was the person originally in the cell next to his. If they agreed to help her, Alex promised, she would give them a boat to leave Hydra Island.
The three arrived at the small building bearing the Hydra logo on the main doors. Inside, Karl was found in
Room 23, restrained to a chair and wearing LED glasses, being forced to watch a bizarre video with flashing images and words, as well as a loud industrial-sounding soundtrack that seemed to be a form of brainwashing. When Kate and Alex freed him from the chair, Karl was not fully conscious and had to be carried out by Sawyer.