Corky Romano (CHRIS KATTAN) is a mild-mannered and good-natured veterinarian who believes that his father, Pops (PETER FALK), is in the landscaping business. Thus, he's shocked when he gets a call to visit him and learns that his father, his right-hand man Leo Corrigan (FRED WARD), and his siblings, Paulie (PETER BERG) - the functionally illiterate brother - and Peter (CHRIS PENN) - the repressed homosexual - are all involved in the organized crime world of racketeering, prostitution and underground casinos.
It seems that Pops, who's now fallen ill, has been indicted by a grand jury that has some sort of incriminating evidence on him. Realizing an informant has stung him, he's decided to put one of his own men undercover into the FBI and steal that evidence. The only problem is that the Feds know and can recognize all of the Romanos, except for Corky who was kicked out of the house long ago.
Accordingly, and despite nearly everyone's reluctance to have him be the mole - Corky agrees to pose as an FBI agent, complete with a forged badge and resume. Unbeknownst to Corky, however, that's made him out to be a super agent, and thus Director Howard Shuster (RICHARD ROUNDTREE) assigns Corky to work with Agent Kate Russo (VINESSA SHAW) in catching the Night Vulture, the biggest heroin supplier on the East Coast.
Under the guise of Agent Pissant, Corky stumbles and bumbles his way through one assignment after another - always coming out looking good and/or highly efficient despite himself. He then sets out to find the evidence against his father, all while working with fellow agents Bob Cox (ROGER FAN) and Terrence Darnell (DAVE SHERIDAN), falling for Russo, and finding himself under the suspicious eye of senior Agent Brick Davis (MATTHEW GLAVE) who knows something's not right with the new agent.