Lt. Boma
Don Marshall

Lt. Gaetano
Peter Marco

Lt. Latimer
Resse Vaughn

Lt. Commander Kelowitz
Grant Woods

Yeoman Mears
Phyllis Douglas

High Commissioner Ferris
John Crawford

Humanoid
Buck Maffei

The Enterprise, delivering urgent medical supplies to Makus III, makes a slight detour in order to fulfil standing orders to investigate quasar-like formations. The shuttlecraft 'Galileo' is despatched to explore the phenomenon named Murasaki 312. Heavy ionisation in the area affects the Enterprise's sensors and it loses track of the shuttlecraft which, also affected by the formation, is forced to make an emergency crash landing on the planet Taurus II.

Spock, in command of the expedition, has Scotty start making repairs to the craft while two crewmen are assigned to survey the surrounding area. The Galileo has sustained heavy damage and Scott, despite his best efforts, tells Spock that the weight of the shuttlecraft will have to be reduced by 500lbs in order to be able to achieve orbit. Back on the Enterprise, the planet Taurus II has been identified as the only place where the members of the expedition could survive if they had managed a successful emergency landing.

On the surface, the crewmen sent out to scout around are attacked by giant, hairy humanoids and one of them is killed. Even without him though, the shuttlecraft will still be too heavy. The crew holds a burial service for the man but Spock refuses to take part, considering the repairs to the shuttlecraft to be more urgent, which leads to an increasingly bad feeling towards him. While he is working on the engines a fuel line breaks, spilling enough of the valuable substance to end all hope of achieving orbit. Also, they have now come under attack themselves from the giant humanoids.

Scotty discovers that he can possibly adapt their phaser weapons as an energy source and Spock orders the sacrifice of their only means of defence to give them a chance of escape. Following the death of another crewman killed by the creatures Spock surprises the team by risking his own life to retrieve the body. He cannot understand their response and is equally puzzled as to why his methods, logically applied, have failed to achieve optimum results.

Scotty completes his work and the Galileo eventually lifts of and achieves orbit but Kirk and the Enterprise, put under official pressure by High Commissioner Ferris, have already been forced to resume their medical mission. In a final calculated gamble Spock ejects their remaining fuel and ignites it. The Enterprise sees the 'distress flare' and returns to rescue them at the last moment before their orbit fatally decays.

Despite insisting that the act of ejecting the last remaining fuel was a logical decision, Spock is teased mercilessly by Kirk and McCoy at his very human 'act of desperation'.