Unsurprisingly, since he's been here before and life here was comparatively much easier than on the island, Preston found himself getting accustomed to city life quickly. Without having to worry about survival in the wilderness and other immediate concerns, he fell back into old routines, putting in the hours to try and regain his old form. On the island he could be useful in other ways, and he had started to believe that what had defined him no longer had to. But back in the city he had lost his refashioned purpose again, so he defaulted to going back to what he knew.
In the afternoon, after a quick shower he ventured outside, running the last of the leftover errands he had from when he first arrived. One of those was returning some books to the library - just maps and information about the city and anything else practical that he could find, the important details of which he had long ago committed to memory. Even after all this time, and after everything that had happened, he hadn't been attracted to the thousands of other texts available to him at the time and he wasn't overly interested in the TARDIS's collection, either.
Perhaps it wasn't that unexpected that in the end, the grip of a loaded gun was far more comfortable in his hand than the weight of a book.
In a plain black coat he was a phantom in the shadows cast by the buildings looming overhead. You couldn't fault Preston for being oblivious to the things going on around him - he was fairly aware, in general, but he wasn't paying too much attention to all the details that would have led him to picking up the real ghost, and not the impostor he'd already met, from his past lurking in his vicinity.