The death of a young man off the Scottish coast leads to the Doomwatch team investigating a cover up in the case of a sunken ship, and the discovery of a revolutionary life-changing science.

An inquest is held into the death of a local girl from rabies. How was she infected? A local woman thinks she knows, and she doesn't believe dogs are involved.

A young boy dies while attempting to retrieve a ball from a high roof, but the cause of his death is not from falling. Doomwatch investigate.

An inquiry into Doomwatch is begun following the events surrounding Ridge's breakdown. Meanwhile, Quist is summoned to a large country estate in Scotland, where he finds himself offered a new position with both power and wealth in the private sector, but only if he will curtail his investigations into a new drug called disocyanate. Back in London, the Minister decides that it is time to place his own man within Doomwatch, and so despatches Commander Neil Stafford to join the team.

When John Ridge's father, Wilfred, becomes seriously ill, he decides to devote all his time to looking after him. Wilfred is then taken to hospital and put into the care of Doctor Cordell, but shortly afterwards he dies. Ridge is suspicious, and his investigations uncover a disturbing fact: Doctor Cordell is an advocate of euthanasia.