Stalag 13 has been chosen as the hiding place for an unidentified radar device. It is heavily guarded, but London demands its removal and shipment to England.
After learning of Klink's new affinity for the occult, Hogan convinces Klink that LeBeau was struck by lightning (he actually slipped off the roof in a rainstorm) and can now see the future.
While in session with the Gypsy LeBeau, the heroes are able to rip off the radar device and complete the mission.
The shenanigans carried off by the POWs in this episode are exactly the sorts of scams which make this show a classic.