Recap: A goon named Ted Cardwell makes a photocopy of The WWII West Coast Connection, a research article written by Melba Bozinsky. In the next scene, he hands it over to his goon friend: John McMasters, aka an associate editor of a historical rag. John looks impressed by the article and says that this Melba Bozinsky has thorough intel they've never seen or heard of...and guesses she got help from her good friend, an Austrian historian named Heinrich Von Schlauser who has a seemingly endless of supply of first hand info about WWII. John tells Ted that if he were to publish the article, everyone and their dog would descend on the Pacific Ocean to search for the cache of lost gold...therefore, his plan is to hang onto Melba's article for as long as possible, then return it to her with a letter of regret that cites 'a lack of evidence' as the reason for declining publication. The two cackle with delight at their nefarious scheme to use Melba's research to unearth the gold treasure for themselves.
Aboard the Riptide, the trio is playing Scrabble and lamenting about how bored and broke they are during a current dry spell of zero clients and/or helicopter tours. When they hear someone step onto the boat, they head up to the deck and find a woman wearing funeral attire. She tells them she's in a lot of trouble, then natters about a hired assassin on a train before handing Cody a small falcon statue she wants delivered. When he opens it, a fake snake pops out...and both the woman and Murray dissolve into a fit of giggles. Murray applauds her "great entrance", and the woman - played by Geena Davis! - strips off her veil hat, wig, and shapeless black dress to reveal a smokin' bod. As Nick and Cody openly ogle her, Murray introduces his sister as Dr. Melba Bozinsky, a PhD Harvard graduate. Melba gives Nick and Cody an appreciative once over and declares them hunks, then shakes Nick's hand, which she zaps with a joy buzzer. As Murray ushers her below to get something to eat, Cody tells Nick he's shocked that a dork like Murray could have such a hot sister...and the two agree that to avoid any "stickiness" (pun??), they're going to have to treat her like she's their sister.
Melba tells the trio that her article, The WWII West Coast Connection, was rejected for a lack of evidence, which she thinks is total B.S...and while she's telling them this, she's playing footsies under the table with Cody while winking at him coquettishly. She summarizes the general thesis of her article: during the 1940s, gold bullion was being smuggled out of the U.S. by foreign agents in order to finance Hitler's war effort. Through her extensive research, she learned that a submarine filled with gold left the U.S. coast - but never made it to its destination: the Channel Islands. She pauses playing footsies with Cody to give Nick a sensual head and neck massage (!) and says she's determined to find the lost submarine. Murray's all, "This is sooooo boss!" and also perfect timing for them to get involved in this "case" on account of they have nothing better to do lately except play Scrabble. Melba says that before they do anything, she's going to need to get in touch with her good friend and WWII expert, Heinrich Von Schlauser.
Over at Heinrich's place, Melba tells her old Austrian friend she's pretty sure that a boatload of gold bullion is at the bottom of the ocean somewhere in the Pacific Ocean. He mumbles about how tough it is to find stuff in the ocean, so Murray says they're more than welcome to use his sonar equipment in order to pinpoint an exact location. Heinrich says he's skeptical of "zis pipe dream", but agrees to help in the recovery effort however he can.
After using Mimi to drop sonar buoys in the ocean, they take the Riptide out to sea to closely monitor the sonar readings. As Murray taps in the coordinates on his computer, they're startled to hear a loud pop above deck and soon realize that a helicopter is hovering over them as someone shoots at them with a machine gun. Nick grabs his gun and suggests they flee aboard the Ebb Tide (which seems far less safe than taking cover inside the Riptide, but OK) ... and as they motor across the open water [and somehow avoid getting hit by the constant spray of bullets], Nick returns fire on the helicopter and pierces the fuel tank, forcing the bad guys to retreat whence they came.
Back in King Harbor, Nick and Cody patch up all the bullet holes while Murray says he'll work on finding out who was piloting the attack helicopter. Melba gazes at Nick and Cody with a dreamy look of admiration and tells them how terrific they are to be such good friends to her dorky brother. She says that, unlike the friends he usually hangs with, they're handsome and virile...then gives them both a long smooch before going below to join Murray on the computer. Cody and Nick stare at each other in shocked wonderment at that PDA weirdness, then get into a scrap about the "special vibes" each of them believes Melba is sending specifically to him. As they argue about that, Melba makes a sudden announcement about a new location for where the sunken sub likely ended up.
As the trio + Melba and Heinrich heads out to sea again, Murray taps away at his computer and quickly learns that the helicopter that attacked them was rented out to a man named John McMasters. Melba suddenly squeals excitedly when she sees something interesting appear on the sonar monitor and says she'd like to dive down right now to see if it's the lost sub - but the trio warns her that it's too late in the day and therefore much too dangerous to go diving in the dark. She mulls that over and agrees, then suggests they return to King Harbor and put on their dancing shoes for a fun night of boogying!
Ted tells John that now that Melba and Heinrich are involved in the search for the lost sub, he wants to kill them and anyone else who might know about the gold - but John suggests it'd be easier to let Melba live long enough to find the gold, steal it from her, and then kill her and everyone around her. He recalls that the name of the boat they shot at is the Riptide, and that they should creep onto it while no one's there and see whassup aboard the floating detective agency.
Murray shows Nick and Cody photos of himself and Melba as children...and everyone gushes over their adorableness. Heinrich declines an evening out and says he's going home to rest...and Melba throws a fake rubber snake at Nick and then giggles devilishly, which freaks him and Cody out and makes them seriously rethink her appeal. As they glare in Melba's direction, she happily announces that she's ready to go out to dinner and get started on that boogying.
At Straightaways, Melba is coaxing Nick to boogie more enthusiastically than the awkward looking side shuffle he's currently doing. From the table, Murray remarks to a sour looking Cody how cute Melba and Nick look together and that it'd be great to have Nick as a brother-in-law. Max ambles over and informs Cody and Murray that she just saw someone skulking aboard the Riptide, and they're all, "Wuh?" and race off to find out who the intruder is.
Ted and John are poking around the Riptide when they see the trio + Melba coming and abscond on a speedboat. The group rushes aboard to see if anything is missing, and Melba finds what looks suspiciously like a bomb. Nick and Cody assume she's playing another of her infantile pranks on them, so Nick takes the bomb and half-heartedly throws it overboard...where it explodes a few seconds later. Oops.
Lieutenant Quinlan grumps over to the Riptide and rails at Nick for "throwing a bomb in the water for jollies" and accuses him of doing it for the pure joy of scaring the bejeezus out of everyone in the harbor. Melba stares at the buffoon in complete incredulity and tells Murray he's "hysterical" ... and Quinlan glares at her and asks Murray who "this bimbo" is. As Melba giggles and calls him "too cute", Murray haughtily informs Quinlan that this bimbo is Dr. Melba Bozinsky, then implores him to consider functioning like a cop and maybe look into who planted the bomb on their boat - the likeliest suspect being John McMasters, the guy who opened fire on them from his rented helicopter. Quinlan rolls his eyes and asks what they did to make the man shoot at them (!) and Murray clams up and says he's not at liberty to say. Quinlan - who, by this point, should probably give up the charade of policing altogether - says he really couldn't give a rat's ass that some crazed gunman (and alleged bomb maker) is out there trying to kill Melba and/or the Riptide trio and announces that he's going home and back to bed. Once he's out of hearing range, Cody suggests they do their own investigating into the historical magazine that Melba submitted her article to...so Murray punches something into his computer and discovers that John McMasters is the associate editor of the historical rag. From this, he and Cody quickly deduce that McMasters probably wants to loot the gold bullion from the sunken WWII submarine - and Melba shrieks at the collective genius of the Riptide Detective Agency for figuring out a motive she should have twigged onto when a gun toter on a helicopter appeared at the exact location she outlined in her article was the site of a sunken treasure. She rewards Cody with a long, hard smooch.
As Operation Provide a Decoy To Fool the Bad Guys gets into motion, Nick lands Mimi on a nearby remote island and waits for word from Cody.
Ted and John are flying around on their rented chopper, once again scanning the ocean for the Riptide. Cody is aboard the Ebb Tide by himself, floating around the previous sunken treasure site, 'cause apparently the plan is for Nick to blast over on Mimi to launch a chopper-on-chopper attack on the bad guys and put them out of commission for good. Sounds just crazy enough to work.
Murray tells Heinrich and Melba he's pretty sure he now has the correct coordinates for the lost sub, and Melba excitedly puts her wetsuit on so she can leap into the ocean and start searching through the wreckage.
When the bad guys' helicopter appears on the horizon, Cody radios Nick, who assures him that he and Mimi will be there, pronto. When he finally gets the decrepit old bird airborne, he flies over to Cody's location, opens fire on the bad guys' helicopter and punctures their fuel line. The bad guys are all, "Ack!" and are forced to make an emergency landing on the nearby remote island.
Nick and Cody land on the island and subdue the bad guys at gunpoint. Ted begs to allow them to work something out...but when they're accused of planting a bomb aboard the Riptide, Ted and John are all, "Wuh?" and insist they didn't have anything to do with any bomb, and that they can't begin to guess who else would want them all dead since they haven't told another soul about the sunken treasure. Nick and Cody decide they're convinced of Ted's/John's innocence about the bomb and mull over the possibility that Heinrich Von Schlauser is the bomb planter.
Melba is easily able to locate the sunken submarine...and we get a lot of superfluous underwater footage of the vessel's decomposing interior. Melba finds a large safe where the gold was likely stashed, then signals to Murray and Heinrich that they can begin reeling it in. When the safe is safely aboard the Riptide, Heinrich pulls a gun on Melba and Murray and says, "I vas hoping it vouldn't come to zis."
Nick and Cody scramble to get decrepit Mimi into the air to race over to the Riptide in the nick of time. They try radioing Murray, but get no reply.
Heinrich ties up Melba and Murray, back-to-back with cartoonishly thick rope, and explains to Melba that her landmark discovery of the WWII submarine has made "certain conclusions necessary". He says that while he's extremely fond of her, the only thing that's ever meant anything to him was the "glorious Third Reich and Mein Führer". Melba and Murray are all, "Seriously, dude? The war's been over for decades" - but Heinrich says that, as incomprehensible as it may sound in 1984, duty calls. And by duty, he means he's going to destroy the safe, the boat, them on the boat - and only then will the war finally be over for him. He caps off his nonsensical blather with a Heil Hitler! Nazi salute, then places a bomb atop the safe, nods a curt goodbye to Melba, and hops aboard a dinghy to flee the impending explosion.
When Murray hears Nick and Cody attempting to call them on the radio, he turns on Roboz with a voice command and instructs the orange bot to pick up the radio receiver so he can loudly inform Nick and Cody that they're tied up and about to be blown to smithereens. With only seconds to go before the bomb is set to detonate, Mimi arrives at the Riptide's location, and Cody leaps aboard, throws the bomb as far away as he can, and watches it explode in the ocean. Phew!
Nick, meanwhile, chases Heinrich down with Mimi and bellows on his speaker system, "It's over!"
Melba wraps up the episode by informing the Riptide trio that no gold was found inside the safe, just some boring paperwork revealing details about the impending Normandy invasion. Melba solemnly points out that since the Germans never received this intel, the outcome of WWII was forever changed. Nick mulls over this fictional retelling of the war, then pretends to drop the historical papers from the safe overboard...and when Melba dives into the water to retrieve them, he's all, "Haha...you fell for my lame prank", and everyone chuckles at the well deserved payback.