The vanishing death

Thieves, breaking into a mortuary to steal the body of a woman, are disturbed by a police constable, and they escape, dropping their burden in the street. Then, days later, a lorry grazes a speeding car, dislodging a hamper attached to its roof. Neither vehicle stops. Inside the hamper, the police find the body of a recently murdered man whose corpse had been stolen whilst awaiting police examination. Who's behind the would-be body-snatcher - and what is their sinister purpose ...?