The United Federation of Planets sends the U.S.S. Enterprise to Gideon, in the hope that the Gideons will become a member. The planet Gideon appears to be a haven — the inhabitants are healthy and no one seems to ever die in the totally germ-free environment. Reluctantly, the Gideon council allows Captain Kirk alone to beam to their council chamber, and he transports off the ship. Kirk finds himself on his own ship, where all of his crew have seemingly vanished, except for a Gideon woman, Odona. Kirk realizes that the ship is fake, and when Odona becomes ill, the Gideons' plan is revealed: using Kirk's blood, Odona was infected with a disease which Kirk had recovered from. The infection is fatal, and the Gideons hoped to spread it across their world to reduce the population.

James Doohan (Lt. Cmdr. Montgomery Scott)
Sharon Acker (Odona)
David Hurst (Hodin)
George Takei (Lt. Sulu)
Nichelle Nichols (Lt. Uhura)
Walter Koenig (Ensign Pavel Chekov)
Gene Dynarski (Krodak)
Richard Derr (Admiral Fitzgerald)

• Gene Dynarski also played Ben Childress in "Mudd's Women" and Cmdr. Orfil Quinteros in the TNG episode "11001001".