The Frightened Man — Gerald Verner

Samuel Coyne sends his ward Diana to enlist detective Paul Rivington as a bodyguard because three attempts have been made on his life. Although he denies knowing the attacker's motive or identity, he has erected elaborate defenses around his house. Paul arranges for his brother and partner Bob to take on the job. Later, Bob captures an intruder on the grounds, who recognizes Coyne as somebody he calls Kilroe. Surprisingly, Coyne lets the man go, not wishing to prosecute. Then they discover that Diana has mysteriously disappeared...