One day at work, Tom accidentally injected himself with the serum. The next day he felt so good that he put some in his tea. He started to hear voices — the fish were asking him to stop injecting them. The Sixth Doctor and Peri arrived and offered to help him.
The next morning at work, he made his farewells to the Doctor and Per. He drank his tea, not knowing that Peri had put something in it. His headache cleared and he stopped hearing the voices. (PROSE: The Stabber)