Whilst he is exploring an asteroid Koenig is taken over by an alien race known as the Kalthon, who replace him with an exact double. In consequence every action ordered by the fake Koenig is solely for the benefit of the Kalthon and to the detriment of the welfare of the Alphans. Helena realizes that something is wrong when 'Koenig' is cold to the touch and needs to convince the other crew members.

Ship's engineer Patrick Osgood believes he can obtain titanium, to make a new heart for his sick wife Michelle, from the catacombs of the moon, using dynamite. The explosion which follows gives him a vision of the future in which the ship is pursued by a fireball and this comes true. Though Helena is making a new heart for Michelle, Osgood becomes impatient and drags his wife back into the catacombs, giving Koenig a double task - to avoid the fireball and save the Osgoods.