In a jewelery shop, Rocko (Dan Seymour
) and Mousey (John Harmon
) have the owner tied up on the floor and are proceeding to grab gems when a robot enters and a voice from a speaker tells them to drop their guns - they're under arrest. They try shooting, but the robot keeps coming. The jeweler manages to kick an alarm button, and the robot begins to behave erratically. Horatio Hinkle (Lucien Littlefield
) enters with a portable control console, but the robot keeps swinging its arms wildly. Finally, Hinkle crawls to it and pushes an off button, by which time the robbers have run off. Hinkle hears sirens and thinks everything is going to be all right. From his jail cell, Hinkle protests that he's a graduate of a detective correspondence school and an Ohio correspondent for the Daily Planet
. The police officer (Herman Cantor
) at the jail says he and his robot, Hero, are suspected of taking $60,000 in diamonds. Clark, Lois, and Jimmy arrive with authorization for Hinkle to be released into Clark's custody. Clark announces that Hero has been stolen from the police garage, and that Hinkle must stay at Clark's apartment, with Jimmy for company.
Meanwhile, Rocko and Mousey have taken Hero and are showing it to their boss, Chopper (Russell Johnson
, Gilligan's Island
's Professor), but they don't know how to use the control panel. Chopper gets a phone tip that Hinkle is at Clark's apartment, so he calls there and tells Hinkle he can have his robot back for $100 if he comes alone to a rendezvous. Hinkle pretends to drop a small smoke bomb with a brief knockout effect, rendering Jimmy unconscious long enough to permit an escape. When he recovers, Jimmy rushes to Perry's office, where he interrupts Clark defending Hinkle to Perry and Inspector Henderson. Jimmy tells what happened, and Perry angrily demands for them to find Hinkle and Hero. This sends Clark, Lois, and Jimmy running out, to the amusement of Henderson. Perry turns to him and says "Well?" in a way that has the inspector running too. Clark decides to go with Henderson to the station to hear what the jeweler has to say, while Lois goes to Clark's apartment to wait for a phone call. (She doesn't need to be given a key.)
The rendezvous with Hinkle was a trap, of course, and Chopper demands that Hinkle fit Hero with an oxyacetylene torch, so he can open the vault at the Metropolis Trust Company and steal $10 million in cash. The crooks stick Hinkle and Hero in a small room, leaving Rocko as guard outside, while Chopper and Mousey go to get oxygen tanks for their plan. Once left alone, Hinkle removes a key from his heel and unlocks a panel on Hero, retrieving a radio. He calls XP127Y4, actually his assistant Marvin (Robert Easton
), and tells him to contact Clark and give him the address where he's been taken. Before he can elaborate, he hears Rocko unlocking the door, so replaces the radio. Rocko is suspicious, and removes Hero from the room.
Marvin calls Clark's apartment, and passes on the address to Lois. She asks if Hinkle sounded worried, but Marvin says he sounded as happy as a pig in a watermelon patch. Lois goes to the address, where she is immediately caught. Chopper forces Hinkle to cooperate in his scheme by threatening to have Rocko work over Lois with a hammer. Later, the crooks are looking over Hinkle's shoulder as he monitors Hero's progress. The robot burns through the vault door and takes the cash, then starts back. The crooks step away to have a celebratory drink, giving Hinkle the chance to have Hero begin pulling every fire alarm he comes across. Fire trucks race to the area, and in Clark's apartment Jimmy and Clark hear the sirens. Clark calls the fire department and learns they're false alarms, set by a robot. Clark tells Jimmy to rush to the area (while Clark apparently goes back to bed?)
Back at the hideout, Hero has returned, and Hinkle has him take a punch at Chopper. At this, the crooks grab the control panel from him. Mousey says he's been watching Hinkle and can operate the controls. He sets the robot after Hinkle and soon has him on the floor, about to be stomped on. Lois screams, so Mousey turns Hero on her to shut her up. At the last second, Superman arrives. Hero attacks him, but ends up as a pile of parts on the floor. Superman quickly dispatches the crooks and picks up Lois, saying he'll return for the unconscious Hinkle later.
Lois and Jimmy enter Clark's apartment as Clark enters from his bedroom. Hinkle wakes up, wondering how he got there. Henderson arrives and demands that Hinkle produce the stolen diamonds. Clark reaches into the junk that used to be Hero and pulls out some diamonds. Lois wonders how he could do that, but Clark says he was just lucky. The inspector thinks there might be more diamonds so starts looking through the junk. A random burst from the torch gets him in the rear end, provoking laughter from the others. Henderson shouts "Anyone who thinks that's funny is going to the station right now." The others suppress their amusement, but just barely.