"Gamble your cares away, on beautiful McHale's Island, the Las Vegas of the Pacific. Open to all eligible Servicemen (Those with money). P.S.: Burn this invitation after reading." Reads the invitation to 'McHale's First Annual Gaming Festival', printed on the backs of Mother's Day cards, which are to be distributed throughout the convoy, which is to dock, on Mother's Day. McHale has agreed to the huge blow-out, with games, food, drink, and dancing girls, as long as the games are conducted on the up-and-up.
Later, in his office, Binghamton is using a Dictaphone to dictate a Mother's Day letter to his 'Mums', when he is interrupted by Ensign Parker. Parker is Officer Of The Deck, for the day, and, just as he reports for duty, Binghamton receives a phone call, asking him to come to the Supply Depot. Leaving Parker in charge, Binghamton heads out, warning Parker, on the way, not to make any Command Decisions. When Binghamton is out of sight, Parker takes a seat at Binghamton's desk, and soon spots the Dictaphone. Purely as a joke, he dictates a letter to the Secretary Of The Navy, with the idea of choosing, at random, some Mothers of some of the Fighting Men Of The Pacific, and bringing them out to visit their Sons, for Mother's Day, and uses the Crew of the PT 73 as an example. But, when he hears Binghamton coming back, Parker quickly shuts off the machine, gets up out of Binghamton's chair, and pretends to be busy at the Captain's safe, as Binghamton walks in. Binghamton orders Parker to take a box of cookies to the airstrip, to be delivered to The Admiral. But, before he leaves, Parker steps to the Dictaphone, and tries to erase his recording. But Binghamton orders him away from the machine, and to get those cookies to the airstrip, on the double. Parker leaves, and Binghamton sits down at his desk, closes his letter, on the Dictaphone, and orders it to be transcribed.
Later, Parker's letter has made it's way to the office of The Secretary Of The Navy, in Washington, where a Captain Bryce (Dan Frazer) is discussing the letter with The Secretary. Bryce thinks that Binghamton has lost his mind, but The Secretary likes the idea, and orders Bryce to put the plan into action. Meanwhile, on McHale's island, the boys are putting the finishing touches on their Gaming Festival. At the main base, Binghamton is preparing for the arrival of the convoy, but has a feeling that something is up, with McHale and his men, for they've been quiet, all week. He braces himself for the worst, when his office phone rings. Carpenter takes the call, and relates to Binghamton, the news that a Captain Bryce has just landed, at the airstrip. Later, after Bryce arrives, Binghamton is somewhat shocked to hear that The Secretary Of The Navy liked his idea. But, unaware that he'd presented any ideas to The Secretary, Binghamton asks Bryce which idea he's talking about, and, when Bryce tells him about the Mother's Day surprise for the Crew of the PT 73, Binghamton's suspicions are confirmed.
Back on McHale's island, the boys are ready for the arrival of the Convoy Sailors, with all the game tables, food, and decorations in place, when Fuji rushes in to report Binghamton's approach. Parker frantically calls 'Condition Red', and he, McHale, and the boys quickly hide the gaming equipment, and, at the last second, McHale uses a large cake to cover the roulette wheel. Meanwhile, Binghamton has come ashore with Mrs. Parker (Carol Veazie), Mrs. Bell (Tinker's Mom – Cheerio Meredith), and Mrs. Gruber (Naomi Stevens). All are surprised to see the ladies, especially Parker, Tinker, and Gruber. Tinker introduces his Mom to McHale, who asks what brought them to Taratupa. Mrs. Bell replies that their 'Nice Captain Binghamton' sent for them, as a Mother's Day surprise. Binghamton soon enters, and, while he hams it up for the Photographer who has come along, Parker introduces his Mom to McHale. Binghamton soon joins, for another photo, with Parker and his Mom, and makes sure that McHale isn't a part of it. Meanwhile, Gruber is shedding tears of joy, over seeing his Mom, and Binghamton has to get in on that photo opportunity.
The ladies soon see the decorations and food, and suspect that they were expected. McHale tells them that they weren't expected, and that the food is for their usual 4 o'clock snack. Binghamton suspects that McHale is behind the whole deal, but lets McHale off the hook, since the situation has generated so much positive attention.
Mrs. Gruber invites the boys to have a piece of cake, and McHale panics, for he knows that their scheme might be discovered. McHale diverts their attention, by suggesting that the ladies get some rest, after their long flight. Captain Bryce agrees, and he, Binghamton, and the Photographers leave.
Later, the boys are discussing the situation, in McHale's hut, and can't figure out how the Mothers got invited. After they dismiss the idea that it was Binghamton's doing, Parker brings up the fact that he'd had the same idea, the week before. Knowing that the convoy Sailors will be arriving soon, for the big shindig, McHale quickly comes up with a plan, to keep The Ladies from finding out what they're up to.
Later, after a big dinner prepared by Fuji – Whom they pass off, to the ladies, as their Filipino Houseboy, 'Irving' – Parker announces that the ladies will soon be shoving off on a sight-seeing tour of the harbor, on The 73, with their Sons. McHale and the rest of the boys are relieved, when they're out of sight, but Virgil soon rushes in to report that some of the native girls, whom they've invited to the big party, have arrived.
On their way out, the boys and the ladies run in to the girls, and the ladies want to know who they are. Tinker explains that they're 'Native orphan waifs', and Gruber adds that they've come to do the laundry. But, when the ladies see how skimpily dressed the 'waifs' are, they insist on taking the girls with them, to see that they're properly dressed.
Shortly later, the Sailors and Marines begin to arrive, for the big party. McHale steps in, as the first boatload arrives, and takes them aside, to explain the situation, while, in Binghamton's office, Binghamton is reading one of the invitations to the party, which Carpenter has found. Immediately, Binghamton suspects that McHale planned the whole Mother's Day thing, to cover for their gambling party. He and Carpenter leave, immediately, to go after McHale, and take Bryce and his Photographer along, so that The Secretary Of The Navy will have proof of the goings-on. Once on McHale's island, they walk in on a party. But... Not the kind of party that Binghamton was expecting.