A sonic mine blows up The Doctor and the Companions on a planet called Seffilun-27 and a medic rescue ship picks them up to transport to a base for recovery. The Doctor is frantic to get back to Seffilun-27 and the T.A.R.D.I.S. but is brought around to the realization that the ship is carrying a patient about to give birth and another with a tricky medical condition. While traversing some dangerous space, something breaches the shields and enters the ship, destroying sensors and power grids wherever it goes. It causes the death of one of the medics and wrecks The Doctor's sonic as well. Identified as a Pting, the people left aboard the ship need to solve three problems -- the Pting itself which is virtually indestructible and has skin toxic to the touch; getting the ship back to the base faster than the automatic routing will allow for; and preventing the ship's controllers at the base from automatically blowing up the ship as a precaution if the presence of the Pting were to be known.
Meanwhile, Yaz and Ryan discuss the concept of fatherhood in relation to Ryan's absentee father and later Ryan and Graham act as doulas for the birth of the Gifftan male.
General Cicero and her brother have a rough relationship but his skills as an engineer and hers as a pilot come together to deliver the ship safely to the base. Sadly, the General gives her life for this final flight.
Ironically, the auto-destruct system turns out to be the lifesaver as the bomb serves to lure the Pting to an airlock from which The Doctor is about to return it to space.