In the early hours of a Tuesday morning in Birmingham, a man rings 999 to say he has killed his flatmate. The man is covered in blood when he is arrested outside his home, and he has a bleeding injury to his hand. He is taken into police custody to be interviewed, where he claims the victim went to stab him with a knife after an argument broke out between them. The injury to his hand was caused when he snatched the knife from the victim in an act of self-defence. The investigation takes a significant turn when digital forensics experts discover a voice note on the suspect's phone which suggests he was involved in an incident earlier that day and sustained the hand injury hours before the fight with the victim even took place.