The Fortress is the 15th produced episode and the 6th broadcast episode of the television series Joe 90.
Joe 90 has the formidable task of finding a microfilm hidden in a remote jungle. If it falls into the wrong hands, it will blow the covers of every W.I.N. agent in the area.
W.I.N. agents Laramie and Fleming, working in the Santa Marina section of a Far Eastern jungle, receive a vital report on microfilm. When they are ambushed, Laramie succeeds in transferring the film to Fleming - but Fleming is tracked and captured. In the nick of time, however, he gets a message through to W.I.N. headquarters but is trapped before he can say where he has hidden the film. Fleming is held prisoner in a virtually invincible fortress, and Laramie lies in a coma. The situation is serious. If Fleming is forced to talk and the microfilm is found, the covers of every W.I.N. agent in the area will be blown. There is just one chance, and that is to give Joe 90 the brain patterns of Mike Laramie from a previously-taken tape. With these, Joe will possess Laramie's vast knowledge of the jungle rivers and the fortress. Joe is flown out to the Far East and gets into the fortress. Once there, he finds that Fleming is being subjected to vicious cross-examination. His torture has left him almost unconscious, but once he is convinced that Joe is a W.I.N. agent, he manages to get as far as the window of his cell, and Joe helps him down to his waiting hovercraft. Ducking shots from the guards, they make their escape, and then comes the torturous journey through the jungle to recover the microfilm which Fleming has hidden. They are tracked by guards all the time, but Joe is able to outmanoeuvre the enemy.