Nikki attends the suicide of a young man. But then all hell breaks out someone is on some sort of a killing spree on the streets of London. The killer is found, a paranoid schizophrenic who has been allowed out into the community.
The killer kills himself in the police cells and tox reports on both his body and the earlier suicide reveal that they have the same cocktail of drugs in them. Both men were in the same Care Centre. A further suicide victim from a few weeks ago also has these drugs in her body, but she had no connection with the men.
Harry discovers that the deaths are connected by an on-line pharmacist, who is supplying fake drugs. She provided the final link in the case to the source of the drugs and he is arrested and charged.Overview from themoviedb.org