Waterskiers off Waikiki discover a body which turns out to be a cop named Bradley, working undercover for Five-O investigating the Island drug trade. He was shot in the back. McGarrett suspects this is work of Surfer (Nephi Hannemann) who works for Martin Lynch (Vic Tayback).
McGarrett decides to use an operative not from Oahu to carry on with the investigation. He flies to Maui where he meets with Chief Sato (Ernest G. Chan), asking for a volunteer who is "experienced and unknown." Chief Sato introduces McGarrett to Valerie Bates (Carol Lynley), who spent three years with LAPD before she moved to Hawaii. McGarrett resists, saying "this case is much too heavy for a lady." He finally relents and accepts her after she insists "I am a damn good cop."
At Lynch's house, Kimo Hameo (Enrique Novi) says he didn't want to get involved with Lynch's drug dealings if murder was going to be involved. Surfer tells Lynch that Kimo can't take the pressure.
Valerie, using the pseudonym Karen Baker, meets Kimo at a beachfront bar as Danno watches. After she leaves to get changed, two cops who look like narcs (part of McGarrett's plan) arrive asking for her, prompting Kimo to leave. Outside, the two of them flee the scene. She says the cops were after her because she was trying to deliver cocaine for someone on the mainland.
At Lynch's, Kimo tells his boss that Valerie is cool -- "she's one of us" because she's "in trouble herself." Surfer checks a sample of coke in her purse, and both he and Lynch tell Valerie she's really dumb carrying drugs around. Lynch leers at her, "It's a good thing you're a pretty girl." He tells Surfer to check her out.
Valerie and Kimo frolic at the beach, talking about Kimo's friends.
At the Five-O office, a TV newsman, Jimmy Akana (Doug Mossman) is pushing McGarrett for details about Bradley's death. McGarrett tells him to keep a lid on his reporting for a few days.
At Lynch's, Valerie plants a bug on a phone which will be monitored by Chin Ho in a van parked outside. Surfer almost catches her. Lynch learns from Surfer that "Karen's" mainland record for a couple of drug busts checks out. Akana reports that a body was found in the harbor, but its identity is unknown.
McGarrett talks to the Coast Guard about the movement of ships coming from Hong Kong to Hawaii. The suspected value of the drugs has upped to over $25 million.
Lynch is disturbed by the fact that no news of Bradley's death has appeared in the media.
Valerie stays overnight at Kimo's mother's house. Following this, they go to Kimo's uncle's woodworking shop where Kimo shows her carvings which will be used to smuggle the drugs to the mainland. Valerie asks Kimo about his "friends," wondering why he associates with them. Kimo says that Lynch paid off some of his gambling debts. She challenges Kimo to "do something about it."
Via the bug in the phone, Chin Ho learns details of the heroin drop, such as the name of the boat and time of arrival.
Kimo tells Lynch that Valerie is "in" on the deal, that they are now partners. Lynch says that her share of the money will come out of Kimo's. Later, Kimo finds the bug which Valerie planted in the phone, but hides it when Surfer enters the room.
Kimo is furious, having found out that "Karen" is actually a cop. She tells him to "play this one through with me," and that she will testify on his behalf in court.
Surfer discovers that "Karen's" background is phony. Lynch says he will arrange things so Kimo kills her after the drop.
As they all leave Lynch's, Chin Ho signals to McGarrett, who tails them by helicopter. The drug drop is made at the beach, and everyone gathers at the woodcarving shop. Surfer tells Kimo that "Karen" is "doing a number" on him and challenges Kimo to shoot her. As the two of them struggle, Valerie hits Surfer on the head with one of the wooden statues.
Outside, Lynch is quickly apprehended by Five-O and HPD. With Surfer in pursuit, Kimo and Valerie flee through a sugar cane field, with McGarrett in the helicopter above. Surfer shoots Kimo in the back and McGarrett jumps from the copter to apprehend him.
Kimo succumbs to his wounds in a tearful farewell scene with Valerie. McGarrett compliments her, saying "a great job, lady."