Tobbs exits the airlock into space to investigate a power failure. He pulls himself along the ladders, ignoring the safety procedures by not tethering. The section of hull has ridged white domes on it, which Tobbs dubs space barnacles. On the comms, Locklear says the suit's life support is losing power, and is cut off. The barnacles jump on to Tobbs, blocking his view and cracking the glass of his helmet.
On the flight deck of the Godspeed, the crew assesses the situation. Tobbs is dead and power is at thirty-five percent and falling. Locklear tells Thelesa to send out a distress signal, but there's not enough power for more than a few seconds.
The Ninth Doctor strolls in, and says he is going to save their lives. He sonics a display, and it shows the ship's hull covered in barnacles. Locklear orders Keinholz to fire at them. Each time he fires, however, more of the creatures appear. The Doctor explains they're feeding on the energy from the ship and the blasts and converting it into mass to reproduce.
Locklear asks the Doctor what they should do. He will only tell her if she agrees to leave the system and tell her company there was nothing there. She agrees, and he tells her to shut the ship down and make the barnacles think there's no energy left. Keinholz shuts off everything, including life support.
The Doctor goes to the TARDIS, and Locklear follows. He materialises outside the Godspeed and throws open the doors. He flashes the light on top of the TARDIS, and one by one the barnacles drift towards it, coating the exterior. The Doctor hurriedly dematerialises, taking the sphere of barnacles with him to a nearby asteroid belt. Locklear arrives back on the Godspeed and tells her crew the Doctor has saved them.
- Tobbs has the line, "It's time to leave the airlock if you dare", stuck in his head, misremembering a lyric from "Space Oddity", with "airlock" in place of "capsule".
- This story accompanied a chapter on the TARDIS's energy source.