Mobsters Rocky and Leo are hitting up stores in the neighborhood for protection money. Ballet teacher Jill is unable to pay and they beat her up. Frank is called in to Police Squad! Headquarters by Ed to talk to Jill, but she refuses to testify. They put a tail on her and examine a map of the area, and determine that the reports are focused in one area. Ed suggests that they set up an undercover operation in an empty store.
Frank and Officer Norberg set up in a locksmith shop and set up the business. Rocky and Leo visit and demand money, and Frank refuses to pay. The thugs leave only to open fire on the shop and throw a rock through the window. Frank takes the rock to the lab but Mr. Olson is unable to determine anything conclusive from it. Back at the store, Rocky and Leo return and threaten Frank. He easily tosses them out as the neighborhood shop owners applaud.
Dutch Gunderson, the local mob boss, hears from his underlings and warns that if people think they can fight back, their protection racket is ruined. Dutch sends his girlfriend Stella to the shop and she flirts with Frank, orders a key, and asks Frank to deliver it. She tells him to let himself in if she isn't there. Once Frank figures out the address that she forgot to mention, two weeks later, he stops by and lets himself in. Stella fires through the door but Frank is ready for her and subdues her when she comes out to check. He forces Stella to call Dutch and set up a meeting at 3 o'clock the next day and then books her on an attempted murder charge.
Frank checks with Johnny, who provides him with Photostats that show Dutch is involved in shady business dealings. They won't stand up in court, but Frank doesn't need them for that. He goes to see Dutch and shows him the Photostats, and asks Dutch to become a partner in his protection racket. Dutch, impressed, agrees but tells him to prove himself by killing a tailor that's giving him problems.
Frank calls Ed and Norberg to let them know he'll be at the tailor shop, and they pull out the undercover men at Jill's ballet school. Frank goes to the tailor shop where Rocky and Leo are waiting. They tell him there's been a change of plans and they're going to go after Jill instead. When they enter, Jill calls out Frank's name and the thugs realize that Frank is a cop. Frank disarms them and there's a struggle, and Frank comes out on top. They pick up Dutch and send him to Statesville Prison.