So, first of all, he and Stevens had entered the commercial establishment of Drayne, senior.

There, thanks to Phin's knowledge of the premises, they had made a very good-sized "haul." After that the pair had operated together frequently.

Stevens' junk shop had offered a handy pace in which to hide the plunder.
Then, as time went on, and Phin heard, by chance, that Dick and Dave were trying to catch the burglars in behalf of "The Blade,", a plan had occurred to Phin by which he might ruin Dick utterly in the eyes of the community.
The whole plan had been carefully laid by Stevens and young Drayne.
On this night, just after Conklin's drug store had been closed for the night, Stevens had slipped in a key that had opened a side door for him.

Then the door was left closed but unlocked.
At that hour of the night no one was likely to notice anyone who went in or out at the side door.

And Conklin's was equipped with a public telephone.
Then down to the alleyway had stolen the evil pair.