The Enterprise rescues con artist Harry Mudd and his beautiful female cargo. In pursuit of Mudd's ship, the Enterprise has burned out its lithium crystals, which power the starship's engines, and Kirk orders them to proceed as quickly as possible to the nearest lithium mining planet, Rigel XII. Mudd makes a deal with the three miners to deliver his three women to be their wives.

Roger C. Carmel (Harcourt Fenton "Harry" Mudd)
Karen Steele (Eve McHuron)
DeForest Kelley (Dr. Leonard H. McCoy)
Maggie Thrett (Ruth Bonaventure)
Susan Denberg (Magda Kovas)
James Doohan (Lt. Cmdr. Montgomery Scott)
George Takei (Lt. Hikaru Sulu)
Jim Goodwin (Lt. John Farrell)
Nichelle Nichols (Lt. Uhura)
Gene Dynarski (Ben Childress)
Jon Kowal (Herm Gossett)
Seamon Glass (Benton)
Jerry Foxworth (Security Guard)

• Harry Mudd will later return in "I, Mudd".
  
• The women were "ugly", made attractive by the illegal Venus drug. They revert to their former selves if they go off the drugs. However, when Eve goes off the drug, Kirk tricks her with a gelatin pill and she becomes pretty because she believes she is (which is well-meaning, but absolutely ludicrous).
  
• For some unknown reason, Uhura is wearing a yellow uniform instead of her standard red uniform.