A spaceship is damaged by a meteor. The oxygen supply is not enough for the two men aboard to wait the rescue crew which was on their way. It is enough only for one. Sooner, they should decide who will commit a suicide to give the other a chance (or breathing room) to live.
Obviously no one wants to die but if guided by this rule literally they’ll both cease to exist. One of the two Gartner tries to kill the other Mc Neil by poisoning. But in vain. Mc Neil predicted this even before Gartner thought of homicide. In the end they both spoke philosophically and Gartner understanding his mistake deeply got a poison bottle himself.