Young J. Quincy Pennant is a brilliant but absent minded scientist who has come up with an amazing theory. Unlike skip bombing, Pennant is experimenting with detonating explosives where the shock wave can be sent like a stone skipping over distances without hitting immediate targets, but able to destroy targets at a further distance away, even if they are behind walls. He is sent to a "powder town", a rapidly growing city being built around an arsenal and munitions factory where wartime population growth has brought in criminals, enemy spies and saboteurs.
Accommodations are limited so the munitions factory puts Pennant in a boarding house where he is the only male sharing with five entertainers who work at a local casino run by gangsters. The rambuctious and physically imposing Jeems O'Shea, head of the powder monkeys at the factory, and his sycophant Billy arrive at the house to visit his girlfriend Dolly. O'Shea plays rough with the ladies chasing them around the boarding house and playfully molests them. Only half oblivious to the screaming, Pennant gives a nonchalant punch to O'Shea which due to angle and motion of the blow and throws O'Shea off balance and tumbling down the stairwell where he is knocked out cold to everyone's amazement.
When Pennant reports to the factory, he formally meets O'Shea who at first is surprised that Pennant is not a giant he thought he was. He attempts to intimidate Pennant who is so absent minded he does not understand the threats. O'Shea takes this as extreme nonchalant courage; a quality in demand amongst munitions workers. As Pennant refines his skipping shock wave explosives, the head of the plant gives Pennant his own pistol and assigns Jeems to be his bodyguard.
Pennant falls in love with Miss Sally Dean who also lives at the boarding house but she has been paid by the leaders of the gangsters, Mr Lindsay, to steal the formula but he does not know it.
Mr Lindsay actually works for Dr Wayne but he does not know of Mr Lindsay's runnings with the gangsters.
Things come to a head when Jeems takes the naive Pennant for a night on the town. The muddleheaded scientist is oblivious to several assassination and abduction attempts by enemy agents that Jeems' takes as and admire as an epitome of coolness. Taking Pennant to a casino run by gangsters where his boarding house companions work, Pennant is introduced to his first alcoholic drink that sets Pennant off to breaking the bank of the casino, winning $900 and the admiration of every woman in sight. The chief of the gangsters have his thugs start a brawl in order to knockout Pennant and take back their money but Jeems goes off like a hand grenade where he demolishes the casino and beats up a dozen gangsters.
Dr Wayne, who runs the munitions factory, threatens to fire Pennant when he finds out that Pennant has been gambling and involved with the "gay" women at the casino but Pennant insists he wants to at least continue to see Miss Sally Dean who he has given the secret skipping shock wave formula to for safe keeping.
During this time the enemy agents as well as Mr Lindsay continue trying to obtain Pennant's formula and will go all out to get it. They even involve Miss Dolly, who gets paid $50 to obtain the formula off Miss Sally Dean.
The gangsters then go looking for Pennant at the factory but find O'Shea in the way. They attempt to blow up the factory and set a 5 minute timer with explosives on a cart inside the dynamite room after they bind and tie both O"Shea and Pennant. They manage to flee in an old Buick upon the arrival of Dr Wayne, the guards and the girls as a gun fight embroils.
As they make a getaway down an access lane, O'Shea and Pennant are released by Dr Wayne and the girls. O'Shea and Pennant then only have one minute to remove the explosives from the dynamite store room before it blows up. They push the explosives cart down the hill and towards the access lane, sending the cart crashing onto the getaway Buick in a dramatic explosion.
The two heroes then return to Dr Wayne and the girls who embrace their men, and the movie ends with them kissing after Dr Wayne is shown the coded formula written on a wall in the office of the factory.Victor McLaglen ... Jeems O'Shea
Edmond O'Brien ... J. Quincy 'Penji' Pennant
June Havoc ... Dolly Smythe
Dorothy Lovett ... Sally Dean
Eddie Foy Jr. ... Billy Meeker
Damian O'Flynn ... Oliver Lindsay
Marten Lamont ... Chick Parker
Roy Gordon ... Dr. Wayne
Marion Martin ... Sue
Mary Gordon ... Mrs. Douglas
Frances E. Neal ... Carol
Julie Warren ... Betty
Jane Woodworth ... Helen
George Cleveland ... Gus the Janitor