As his stay in space is coming to an end Roy gets to ride the "Morning Star" as she makes an emergency run to the Space Hospital with a seriously ill man. As Roy and his friends return to the Inner Station on a different ship they become so engrossed in Commander Doyle's story of his participation in the first expedition to Mercury that they fail to notice that their ship is off course: it's heading away from Earth rather than toward it. As they swing around the Moon they refuel their ship from a container catapulted to them from the crater Hipparchus, then they return to the Inner Station after making a short stop at one of the Relay Stations in geostationary orbit to get extra oxygen.