Al Woodruff, if the four men met unexpectedly, would also take it for granted that he was one of them.

They would probably talk to Lone without reserve,--Swan counted on that.

Whereas, if he were present, they would be on their guard, at least.
Swan's plan was to wait at the cabin until he knew that deputies were headed toward the Pass.

Then, with Jack, it would be a simple matter to follow Warfield to where he overtook Al,--supposing he did overtake him.
If he did not, then Swan meant to be present when the meeting occurred.
The dog would trail Al anywhere, since the scent would be less than twenty-four hours old.

Swan would locate Warfield and lead him straight to Al Woodruff, and then make his arrests.