The fresh muddy imprints of a pair of bare feet surprised the two boys.

The explanation behind the mystery was that the bewildered boys had been following a scientist who had just discovered how to make the human body transparent.

The name of the scientist was Griffin. He had carried out a series of experiments to prove that the human body could become invisible.

He swallowed certain rare drugs to make his body as transparent as a sheet of glass. The body also remained as solid as glass.