But Holmes was shaking his head, and his face was puzzled and expectant rather than joyous.

“A bicycle, certainly, but not the bicycle,” said he. “I am familiar with forty-two different impressions left by tires. This, as you perceive, is a Dunlop, with a patch upon the outer cover. Heidegger’s tires were Palmer’s, leaving longitudinal stripes. Aveling, the mathematical master, was sure upon the point. Therefore, it is not Heidegger’s track.”

“The boy’s, then?”

“Possibly, if we could prove a bicycle to have been in his possession. But this we have utterly failed to do. This track, as you perceive, was made by a rider who was going from the direction of the school.”

“Or towards it?”