Dog Island by Sir Arthur Conan Doyle

This gets McInnes ornery. By trade he's an attorney and isn't really built for the gritty life of your average killer or cop. But what he lacks in stamina he makes up for in brains. He foils shifty-eyed and lethal Sonny, for example, with cheese grit bombs folded in a paper napkin and dunked in ice water, startling the killer just long enough for Tom to make an unlikely escape. It's not every day that a hero volleys carbohydrates for justice. Accompanied primarily by the gigantic Joey (ex-cop, ex-FBI, ex-bodyguard), Tom pursues the killers to regional locations that turn deadly: swamps, rusty-roofed oyster shacks, white sand beaches. Tom's an ordinary guy who does extraordinary things, but doesn't have the sort of smug, god-like security that can dull the edge of other, lesser thrillers:

I lost balance and hit the ground chest first. Something dull and hard gouged the side of my neck. Wind rushed out on impact, and I made an involuntary "Oomph" sound. I grabbed for the stick that gouged my neck and pushed. It moved, but in a strange, organic, rolling motion. It was attached to something, and that something was a leg. My hand was wrapped around the dirt- caked toe of a cowboy boot. And I was lying full across someone's corpse.