4. Trial

A retired janitor is killed by a letter bomb, Ronnie and Sam suspect that he may have been killed because he was Jewish. The trace leads to a criminal who was responsible for several similar killings in the '70s, who informs the police that the bomb may have been constructed using an anarchists' guide. As they investigate the janitor's previous place of work, Thameside University, they discover he was fired after false allegations that he was stealing drugs from the Psych lab. They discover that a student who works in the university's postroom, Simon Wells, had recently inquired to other students on how to construct a weapon using mercury – however, after he is arrested, his brief pleads diminished responsibility due to insanity.

Jake and Alesha discover that Wells killed the janitor after he found out that he was stealing drugs and blackmailed him. Wells revealed he decided to create the bomb after a mental condition he had been suffering for sometime returned. Before they prosecute Wells, however, they discover that his doctor, a well respected Marylebone physician, may be responsible for his condition after he failed to continue the correct course of treatment, in favour of money from a drugs company. After it is discovered that Simon is not insane and, in fact, suffers from a brain tumour, his doctor is put in the dock for manslaughter.