Hickory Dickory Dock (S06E02)

Petty thefts are followed by brutal murders at a student hostel in Hickory Road. Even the ingenious 'little grey cells' of Poirot's mind find the circumstances difficult to comprehend. What is the significance of the slashed rucksack, the stolen light bulbs and the lethal morphene tartrate which is substituted for an unsuspecting student's sleeping powder? Only a small mouse bears witness to the ruthless activities of a murderer prepared to go any lengths to conceal the deadly past. (iTunes)