A boatload of men departs from a dock in Honolulu harbor and eventually pulls up beside the Aldebaran, a 1,000-ton cargo ship anchored off shore. After they climb aboard, the men pull out guns and take over the ship. One of the crew, Joey (Beau Van Den Ecker) jumps overboard and attempts to swim away, but he is gunned down by Merkle (John Fitzgibbon). The man in charge of the hijacking, Conroy Baylor (Bruce Wilson) is very displeased by Merkle's trigger-happy attitude.
McGarrett, on a rare day off, is called back into action by Jonathan Kaye, who says the hijacking of the Aldebaran is "priority one." Kaye will not give McGarrett any details as to the ship's cargo.
At the Coast Guard Rescue Center, McGarrett meets with Commander Hawkins (Mark Lenard), who says he got "the same call from Washington." The Aldebaran has a 10-12 hour head start, but only enough fuel for about 500 miles of travel. McGarrett wants to talk to the crew members who were on shore when the hijacking took place. One of these men, Perka (Don Pomes) later says that the captain ran a good ship, but several members of the crew left the ship in Singapore because of disputes over pay and the food.
The owner of the freighter, Zeno Stavrik (Rossano Brazzi) gets in touch with McGarrett from his jet plane. He wonders if the ship has been taken over by terrorists and fears for the ship and crew. He says he has a "special affection" for the Aldebaran. When he arrives in Hawaii, he wants to discuss the hijacking with McGarrett at the Hawaiian Regent Hotel.
On board the ship, Captain Covalt (Nelson Dick Fair) wants to speak to Baylor. When he tries to go to the bridge, Merkle wounds him, incurring Baylor's wrath once again. The crew members and the captain are put in a life raft and set adrift.
McGarrett meets with Stavrik at the hotel, and tells the shipping magnate that the hijackers must know something about Coast Guard procedures. But the top cop is still mystified as to why the ship was hijacked, considering its cargo supposedly consisted of items like furniture, clothing, toys and radios. Stavrik thinks that maybe something illicit is involved, like drugs or illegal aliens. He suggests that the ship will meet another vessel and transfer its cargo, then it will be scuttled.
Chin Ho calls McGarrett and says that when the Aldebaran was leaving the harbor, it almost ran down a fishing vessel. Since it was on a south-southwest course, McGarrett figures that the ship is not headed for the mainland.
The life raft with the Aldebaran's crew members is located by the Coast Guard thanks to its emergency beacon. When McGarrett talks to the men at the hospital in Honolulu, they tell him that they didn't see the boss of the hijacking operation.
A Coast Guard ship finds debris seemingly from the Aldebaran.
Ashore on Maui, the hijackers unload crates from the ship. They know the Coast Guard found the debris.
Commander Hawkins reports an oil slick seen where the ship supposedly went down. He says that it's too deep to try and recover the ship. Hawkins says that Stavrik has started his own search for the vessel. McGarrett wonders why the hijackers scuttled the ship, and why did they set the crew adrift in a raft with an emergency beacon.
On Maui, Baylor and Merkle knock at the door of a low-budget motel. When the door opens, they are greeted by Stavrik, who says, "I wish all my ships were as punctual as yours."
Stavrik tells Baylor to set a course in an open channel, then abandon the ship and scuttle it. He wants the ship on the bottom as soon as it clears the channel. Baylor will receive his payment the next evening. Baylor says he expected to get a command out of the deal. He says this is his "first go at stealing" and that it is hard on his stomach, especially after the killing. He refers to Merkle disgustedly as a "bottom feeder."
From the lab assistant Charlie (Josie Over), McGarrett learns that TNT was detected in the Aldebaran's debris, and the oil slick was actually produced by lubricating, rather than fuel oil.
Back at the office, McGarrett says that he figures the Aldebaran is still afloat, that "we made an assumption [that it had sunk] and that's not good police work."
Jonathan Kaye is on the phone, wondering what's happened to the Aldebaran. McGarrett wants to know what is the ship's mysterious cargo. Kaye finally tells him that it is "highly sophisticated military equipment ... lightweight heavy tank missiles." Apparently even the crew didn't know the cargo. McGarrett wonders if Stavrik knew. Kaye says, "We're not sure," and wonders what Stavrik will say.
The mysterious representative of a foreign government (Ed Fernandez) gives Stavrik a large cheque for the missiles, but puts pressure on him to deliver, saying the missiles are "still a long way from their destination."
In Stavrik's hotel room, McGarrett tells the magnate that he thinks the ship is still afloat, and that the evidence of its sinking was false. Stavrik admits he knew what the ship's cargo was, but that it was "discharged." Danno phones to report that according to the captain, recovering from his wounds in hospital, when the cargo was off-loaded, the captain was ashore and Baylor, chief mate at the time, was in charge of the operation. Shortly after this, Baylor jumped ship. The captain recognized Baylor's voice during the hijacking. Stavrik says he knows that Baylor is an ambitious man who wants his own ship.
After McGarrett leaves the hotel, he gets a call from Kaye in Washington saying that the cargo was never delivered. He says that Stavrik is "double dealing," and that McGarrett should arrest him immediatley -- there is a warrant waiting at the U.S. Attorney-General's office.
However, when McGarrett returns to the hotel, Stavrik is no longer there. The front desk says Stavrik checked out, and his forwarding address is Athens, Greece.
On Maui, the hijackers are relabelling the boxes of missiles as furniture. As Baylor pays off the men, Stavrik drives up. He tells Baylor "We have a problem," and that they have to move up the schedule for the transporting the missiles, moving the trucks to the Maui airport within the hour. Stavrik tells Baylor that McGarrett knows the scuttling was false.
Analyzing maps of Maui, Danno finds a "hot spot" which suggests the presence of trucks. McGarrett orders the Five-O team to Maui immediately.
As the hijackers (minus Baylor and Merkle) attempt to get to the airport, their progress is blocked by a tree in the road. Chin Ho and several cops appear, drawing guns and a battle ensues. All the hijackers are captured, and one is wounded.
At the Maui airport, the missiles are about to be loaded into a cargo jet when McGarrett appears by helicopter. Merkle is now buddy-buddy with Stavrik and tells Baylor that Stavrik "can't afford you any more." When Baylor runs away, Merkle shoots him. Stavrik tries to escape, almost running over McGarrett in the process, but his car is stopped. When pulled out, he says, "I'm a foreign national ... I've committed no crime in your country." McGarrett shows him the missile components inside the "furniture" boxes.
Stavrik is booked, and the wounded Baylor offers to help prosecute him.