Frank and Joe Hardy, his sons, were ambitious to follow in their father’s footsteps, although their mother wished them to prepare themselves for medicine and the law respectively. But the lure of Fenton Hardy’s calling was persistent, and the two boys were bent on proving to their parents that they were capable of becoming first-class detectives. They had given proof of this already by helping their father in a small way on a number of cases, but their first big success had been achieved when they solved the mystery of a jewel and bond robbery from Tower Mansion in Bayport. The story of this has been related in the first and preceding volume of this series, “The Hardy Boys: The Tower Treasure,” wherein was recounted how the Hardy boys solved the mystery of the robbery when the Bayport police and even Fenton Hardy himself were baffled. “I’d rather tackle a good mystery than eat,” laughed Frank. “And here is one right to hand. Let’s go back.” Biff Hooper did not care to seem guilty of cowardice by staying behind while his companions returned to the house, and he was on the point of a reluctant consent when the matter was suddenly solved for them all by a downpour of rain. Storm clouds had been gathering in the sky for the past hour and there had been dull rumblings of thunder. Now an uneasy wind stirred the branches of the trees and rustled dismally among the undergrowth. There was a spatter of raindrops, and then the storm broke in abrupt violence. Rain poured down in sheets. “The motorcycles!” cried Frank. Turning up their coat collars, the boys ran through the thick grass until they reached the place where their machines had been parked. “I saw an old shed near the house,” called out Joe. “We can put the bikes under cover.” There was an abandoned wagon shed near the rear of the house, and toward this refuge the lads trundled the heavy motorcycles. Although the shed was almost falling to pieces, the roof was still in fairly good condition and the machines were safe from the downpour. “Come on,” said Frank, when the motorcycles had been placed under cover. “Let’s go back into the house.” He led the way, running across the open space from the shed, through the driving rain, and Joe followed. The others, after a moment of hesitation, came after them. The back door of the house was open and the lads ran up the steps into the shelter of the building. They were in a room that had evidently been used as a kitchen, and although rain came in slanting streaks through the open windows, the glass of which had long since been shattered, they were at least sheltered from the downpour that had assumed redoubled violence. The rain drummed on the roof of the old house and poured from black skies on the near-by wagon shed. Thunder rolled and rumbled threateningly, and every once in a while a sheet of lightning tore a band of lurid light across the gloom.