In January 1889 the body of Crown Prince Rudolph, heir to the immense Austro-Hungarian empire, was found in his hunting lodge at Mayerling near Vienna. Next to him lay the corpse of his mistress, the 17-year-old Baroness Mary Vetsera. Both of them had been shot through the head. Was it a suicide pact? Was it murder? Why was Mary buried secretly at night? What happened to the gun? How - and why - did Crown Prince Rudolph and Mary Vetsera die?