The detective instinct in him was roused, and his adventurous spirit was alive for action.

First of all, he wanted proof of what MacDonald had told him.
That an attempt had been made to assassinate the old mountaineer he did not for an instant doubt.

But had Joe DeBar, the half-breed, actually betrayed them?
Had he sold himself to Culver Rann, and did Rann hold the key to the secret expedition they had planned into the North?
He did not, at first, care to see Rann.

He made up his mind that if he did meet him he would stop and chat casually with him, as though he had heard and seen nothing to rouse his suspicions.

He particularly wanted to find DeBar; and, next to DeBar, Quade himself.
The night carnival was at its height when Aldous re-entered the long, lighted street.