McNab is an officer of the Santa Barbara Police Department. He is married to a woman named Francine, and is taking dance lessons to prepare for the wedding; he is also anxious about his wedding-night performance, and asked Detective Lassiter for advice on the subject. Because of Lassiter's own marital history, the detective reacted strongly and negatively to the question, and McNab dropped the issue.
Due to Lassiter's reaction, McNab resorted to calling a 1-800 stress-line instead, which resulted in him becoming a target for serial killer Wes Hildenbach. Hildenbach's position as a telephone company technician gave him access to the phone lines leading to the stress-line center, and he intercepted McNab's call, choosing the officer as his next victim. Hildenbach took McNab hostage in his apartment and was about to force McNab to hang himself at gunpoint, but the officer was rescued by Lassiter on a tip from Shawn Spencer. McNab received a cat from Shawn (formerly the pet of Mortimer Tilden, Hildenbach's third victim) as a wedding present.
He first met Shawn when Shawn was called in for questioning regarding his knowledge of several crimes for which he had called in tips. Shawn deduced that McNab was taking dancing lessons and that he was getting married, and McNab accepted the deduction as evidence of Shawn's psychic abilities. He and Shawn have a genuinely friendly repartee that allows Shawn to get to scenes he otherwise wouldn't be able to access.
- "Speak Now or Forever Hold Your Piece"
- "Woman Seeking Dead Husband - Smokers Okay, No Pets"
- "9 Lives"
- "Who Ya Gonna Call?"
- "Cloudy...Chance of Murder"
- "American Duos"
- "65 Million Years Off"
- "Zero To Murder In Sixty Seconds"
- "Meat Is Murder, But Murder Is Also Murder"
- "If You're So Smart, Then Why Are You Dead?"
- "Rob-A-Bye Baby"
- "Bounty Hunters!"
- "Gus' Dad May Have Killed an Old Guy"
- "There's Something About Mira"
- "Lights, Camera...Homicidio"
- "Shawn (and Gus) of the Dead"
- "Disco Didn't Die. It Was Murdered!"
- "Gus Walks Into a Bank"
- "Lassie Did a Bad, Bad Thing"
- "Truer Lies"
- "An Evening With Mr. Yang"
- "He Dead"
- "Shawn Has the Yips"
- "Bollywood Homicide"
- "High Top Fade Out"
- "Shawn Takes a Shot in the Dark"
- "A Very Juliet Episode"
- "Death Is in the Air"
- "The Head, the Tail, the Whole Damn Episode"
- "Mr. Yin Presents ..."