Bobby Brown's grandfather is murdered and no one knows how did the killer enter the locked room?

Excerpt:

"The night of his grandfather's mysterious death at the Cedars, Bobby Blackburn was, at least until midnight, in New York. He was held there by the unhealthy habits and companionships which recently had angered his grandfather to the point of threatening a disciplinary change in his will. As a consequence he drifted into that strange adventure which later was to surround him with dark shadows and overwhelming doubts."