Whether with a doctor on the run, a Bay Area serial killer, or a shady rear-window neighbor, the best whodunits draw us in through compelling characters and the irresistible mysteries that entangle them.

I take comfort in knowing that film noir—a genre that has existed for almost 100 years—has seen it all before. So here are few timeless, hard-won lessons and the noir films that illustrate them.

Here’s the skinny: We put a couple gumshoes on the case to track down all of film noir’s low-lifes, grifters, heels, and molls so we could assemble a lineup worthy of this amazing genre.