- "...You're not as smart as you think you are, and nowhere near as funny," Quirk said. "But you're on the right side of the fence."
- "How do you know it's the right side?" I said.
- "Same side I'm on," Quirk said. - Widow's Walk
Martin Quirk is a Lieutenant in charge of Homicide when we first meet him in The Godwulf Manuscript. He's a big man, "taller and thicker" than Spenser (so probably his height is at least 6'2") who is always immaculately dressed, his shirts ironed, pants creased, and shoes shined. His skin is pockmarked and he has a small scar next to his mouth. His office is austere, with the only object on his desk a plastic cube showing pictures of his family (wife, daughters, and eventually grandchildren).
Quirk is a hard case who, like Spenser, isn't good at diplomacy. He has an exceptionally high success rate in clearing his cases, however. His relationship with Spenser is intially quite adversarial, but Spenser and Quirk recognize in each other a kindred spirit. By Crimson Joy, Quirk trusts Spenser sufficiently to ask for his assistance in hunting a serial killer when he believes the police department to be potentially compromised. By Paper Doll, Quirk actually flies down to South Carolina to rescue Spenser from an illegal arrest.
Quirk is a tough, fair man who takes his job very seriously. Consequently, Spenser frequently irritates him. However, this is true of most people with whom Spenser interacts.
Ace Atkins, in his continuations, promotes Quirk to Assistant Superintendent and introduces more tension in Spenser and Quirk's relationship.