Ship's engineer Patrick Osgood believes he can obtain tiranuim to make a new heart for his sick wife Michelle, from the catacombs of the moon, using explosives. The explosion which follows gives him a vision of the future in which the moon is destroyed by a fireball and a sudden heat storm strikes. Though Helena is making a new heart for Michelle, its repeated failures cause Osgood to become impatient. Convinced he is his wife's only salvation, he drags Michelle down into the catacombs, giving Koenig a double task - to avoid the fireball and save the Osgoods.
- One of the lunar team has visions of Moonbase Alpha being destroyed in a firestorm and takes his critically ill wife deep into the caves beneath the base. Meanwhile, Dr Russell attempts to build an artifical heart to save the woman's life and Cmdr Koenig seeks the source of the heatwave, hidden within a mysterious cloud.