The first book, Smith, was the first in the series I narrated. I've since done five of the seven, and am currently recording the last of them. Two other books, a short story collection, and Harlequin, the fifth of the novels, had different narrators.
Giles has a talent for coming up with bizarre, yet weirdly believable plots that seem designed to relieve DS Smith of his sanity. They certainly seem to relieve him of his holidays. Every time the poor man is due for some time off someone goes on a murder spree in York.
Consider, in the course of the series you'll encounter a revenge killer who very nearly manages to put paid to Smith and the redoubtable DC Erica Whitten, a chameleon-like serial killer who seems literally bent on getting back at Smith for something he didn't even do, a sniper who takes out York's star goalkeeper after he saves a match, a killer clown (really), and even someone who's started sacrificing lonely middle-aged men every full moon.
Smith is a great place to start. The first novel in the series contains the original story, and introduces the continuing characters who'll figure in the rest of the books. Most of them, anyway. It's also a great place to start a new Audible subscription if you don't have one.