Steve and Dan manage to get a discarded ball of tin foil from a giant who tossed it away after eating. This would make a good radioactive shield. The two giants that were eating, just above them, spot them and chase them. A giant praying mantis blocks their escape.
They hide and overhear the two giants mention a government reward which is out for the capture of little people. After the giants leave, Steve wants to go out and regain the foil, which he, followed by Dan, does. Dan, at first, was very afraid of the mantis (oddly neither he nor Dan mentions it as a mantis)---he has been ever since he was a kid. At night, Val tells Steve that since supper is soon--Fitzhugh will be back from the outpost with the larger flashlight Steve needs---even though his hitch there isn't over for quite awhile. Before Fitz can talk Barry into abandoning his post (his watch being set on Grenwich mean time), the same two giants that chased Steve and Dan, mug a third--knocking Fitzhugh over with the fallen giant's hand. Barry calls Mark, Steve, and Val to the scene. After reviving Fitz, who was afraid of lights in his face, they find the victim's fallen watch--an alarm time piece which has enough radium to be a power source, if modified. Mark takes charge and sends Fitzhugh to the ship to help Dan with lead couplers--and Valerie to make sure Fitz doesn't "lose his way." Val mushes Fitzhugh when he tries to get to stay with Mark. Fitz stops to remove a pebble--telling her that they are young people who are so impertinent to his needs. He and Val avoid a wire trap but going two different ways, get separated. Fitz is hung up in a net from which Val rescues him, pulling it down--some kind of animal trap. The party work all night into morning. At morning light, Steve wants to stop working since it is too dangerous. Mark disagrees and he and Steve have a short verbal fight but Betty acts to stop it. Steve and Mark spot a truck with two giants, setting up a sound detector, presumably to find the time piece clock. Mark and Steve cover the clock and stop the others, who were using a makeshift cart (with soda cap wheels) to bring the radium back to camp. Val sees that "those boys have scoop nets and you can be sure they didn't bring them to hunt butterflies." They watch the giants from cover--wondering how to stop the hands of the clock from ticking---if not, the sound detector will pick it up and the giants will find it.
While Fitz dismisses Betty's idea to try to save the clock, he tells Steve they should just wait until the clock runs down, something Steve scoffs at. When Chipper arrives back to them, covered in mud, Mark gets an idea--pour mud in the arms of the clock. Fitzhugh cons Barry into doing their duty to all mankind by sitting and waiting--to which Barry answers, "Yes sir, I only hope mankind will be proud of us." The men try to pry the hands off the clock while the women follow Chipper to a mudhole to collect mud. It doesn't work: the giants get the clock and, despite warnings from an alert Chipper) also get the girls--by dropping a net over the pair.
In a tent, the slow talking giant questions the girls who are in a jar that contains a microphone and speaker. Val gives many flip answers until she learns the giants have other Earth people. Betty devises a way for them to lie and to tell Val this using code of having it sound like "George Washington." Val tells the giant their spaceship is called a "magnetically charged skateboard." When the giant sets them down on some books, Val apologizes to Betty, telling her she is just using flip answers and humor to cover for being frightened out of her mind. Betty tells her she is also frightened out of her mind and hopes it will help her. The others vote to use one of the ship's hydrogen fuel cells to blow up the detector (a small nuclear blast) and save the girls. Everyone votes yes against Fitzhugh, all aware that without the cell they may never return to Earth. Fitz tried to con Barry into voting with him but the boy saw through it and votes to save the girls. Later, when Fitzhugh asks Barry to define discipline, Barry tells him it means saving themselves at any cost and letting Betty and Valerie go hang. Fitz blames it on the youth today--being barbaric. All does not go according to plan. ...but he hangs from the metal detector as the giant searches with a flashlight. Steve stops Dan from trying to help...as they have to be inside the tent to help the girls when and if the blast goes off. Mark hangs from the detector and falls--the giant shines his flashlight in that direction.
Mark, nearly spotted by one of the giants, falls off the detector, injuring his ankle and catching the wire under rock when the huge cord to the detector is kicked up by the giant. Mark, who thought his job was a snap, is now helpless. Steve and Dan saw all this but couldn't do anything about it as they had to get inside the tent. They now wait for Mark to do his explosion. Barry, being extra obnoxious, is getting on Fitzhugh's nerves, even though apologizing. Barry follows Fitzhugh toward the others even though Fitzhugh told him he would not, could not help them on account of his principles. When Fitzhugh sees Barry follow him, Barry tells him if he was just going for a walk, he should have went the other way. Fitzhugh, for a moment, gets angry and almost hits the boy, yelling at him. Fitz doesn't--he takes Barry with him and at first, Barry thinks Mr. Erickson is hurt in the bushes but it is Mr. Wilson. Steve and Dan free the girls from the jar but they all are trapped inside the tent with the giants only half sleeping between them and the way out. To make matters worse, the giants seem to be waking up more. Fitzhugh gets the wire out of the cord and the rock, refusing Barry's help and ignoring Mark's snide, arrogant doubts and comments. Barry urges Fitzhugh on but asks, "You got it free?"---sounding surprised that Fitzhugh got the cord free. Mark tells him, "It wasn't Barry who had the doubts." Fitz answers, "Yes, I presumed that much." He asks Mark if his twisted leg is still very painful. The girls and the pilots are still trapped inside while the giants seem to be waking up, fully. They hide behind the giant books.
Fitzhugh finds himself hesitating to connect the last wires to the detonator battery to blow up the giant device tower---Mark taunts him--telling him after all his long winded speeches and principals, Fitzhugh still cannot sacrifice the cell. Mark drives it home with, "You either destroy that cell or the girls!" Fitz does connect it. The giants rush outside to see what happened after the giant blast. The girls and Steve run out. Dan lingers, drawing a moustache on one of the giants' scale drawings of an Earthman. The next morning, the giants leave the area. Fitzhugh is washing up his face when Barry calls him. "What is it? Can't a man have privacy?" He is speechless when Barry presents Fitz with a homemade reward which reads "hero" on behalf of the crew and passengers of flight 6-12, temporarily delayed to London. Barry pins it to his shirt; the girls kiss him; Mark shakes his hand; and Val tells him the pin and "medal" will cover up a dirty spot on his shirt. Fitzhugh, choked up, thanks them, "Hero, me?" He then moves to Steve and Dan, "We'll find another power source, captain, don't you worry. I always thought there was hope for our situation." Steve smiles and sincerely says, "Thank you, Fitzhugh. That's very encouraging."