Three patients in an Intensive Care Unit die after being injected with digoxin, a drug that had not been prescribed. Each had a faint tattoo on their arm reading 'Let Me Go', implying voluntary euthanasia was involved, though one of the tattoos actually read 'Let Me go Back.' The chief suspects are Dr Elizabeth Walker, an advocate of euthanasia and Carl Burgess, an obsessive ward orderly who behaves oddly. (thetvdb.com)