The Case of the Lying Lie Detector - S1.E40

Blitz can detect lies with great accuracy and barks whenever he hears a lie. However, Blitz was installed (by the crooks) with a device that causes him to do the opposite of what he's supposed to do. Thankfully, it was corrected with the right fixings allowing Blitz to help the C.O.P.S. team rescue Mayor Davis from being held hostage by the crooks.