That's Skulduggery's cue to return to his pacing and/or trip to the library. "Best of luck with that," since he can't smoke and hasn't since at least the early 1700s. "You know how to contact me if you need to. People are... friendly. You should be fine."

Godspeed, secret agent man. Skulduggery is going to have that song stuck in his head for the rest of his day, now...