Space-ship Icarus I failed to kick-start Earth's dying sun back into action and disappeared. Icarus II carries the last available nuclear super-bomb on a mission to try again. The navigator's oversight causes serious damage to the ship, yet returning is no longer a hope, the mission dubious. Having picked up Icarus I's emergency signal from Mercury, they decide to try pick up its bomb. That side-trip comes at a high cost. But an even worse surprise is lurking aboard.