The Crimson Key. Max Malone Mystery, #3

When a dying man presses a blood-red key into Max Malone's hand and whispers, "It unlocks everything.", the Chicago PI finds himself caught in a deadly puzzle. The key leads to a locked room, a hidden fortune, and a trail of bodies - but every answer only raises more questions. As Max digs deeper, he's hunted by gangsters, double-crossed by dames, and shadowed by a killer who will stop at nothing to get what the key unlocks.
In a city where everyone's hiding something, the only thing deadlier than the secret. is the key itself. Some doors should never be opened.