The Man With The Dark Beard

The note left beside Dr John Basted's corpse simply read 'It was the man with the dark beard'. Dr Basted hadn't approved of his daughter Hilary's fiancé. So when Hilary's father is found shot dead inside his own office, the door-key turned from the inside, the fiancé Basil Wilton becomes chief suspect for Scotland Yard. Yet how could the crime have been engineered?