The Lost Stradivarius by J. Meade Falkner

While practicing his violin at Oxford, John Maltravers notices a strange phenomenon: whenever a certain tune is played a mysterious presence seems to enter the room. Maltravers becomes increasingly unsettled, until he makes a startling discovery – tucked away in a hidden cupboard is a priceless Stradivarius! Obsessed with this treasure, he becomes increasingly withdrawn, unaware of the sinister hold this perfect violin is beginning to take over him.