An Australian entomologist named Weatherby (Bruce Wilson) is spotted by Chadwick (Paul Shenar) as he is studying insect life around the roots of a stand of sugar cane. When he tells Chadwick that there is a rare and dangerous infestation in the field, Chadwick kills him.
Chadwick, it turns out, is the plantation manager for Mrs. Katie Holbrook (Carol Vogel). She is a recent widow who, with Chadwick's connivance, is being convinced that she'll have to sell the place to avoid bankruptcy. "Fortunately," a buyer is at hand -- Vadney (Robert Witthans). Vadney claims to represent a group of mainland businessmen who, he asserts, think it would be fun to own a plantation in the Hawaiian Islands. To allay her concerns, Vadney claims that all the workers would be able to stay on. She reluctantly signs an agreement to sell, and further agrees to let independent appraisers set the price.
When Weatherby's body is discovered, the red soil on his boots reveals that he was murdered in a farming area, not where the body was found. It also yields larvae of an exotic cane borer which could wipe out Hawaii's sugar cane crop if not eradicated before the larvae become moths and disperse. Five-0 launches a highly publicized search for the contaminated field.
A worker who observed Chadwick and Weatherby together attempts to blackmail Chadwick. He is killed for his efforts. However, the fact that the worker was employed by Mrs. Holbrook turns McGarrett's attention to her plantation. It soon becomes apparent that Vadney is only a front for Sam Patton (Richard Kiley), an unscrupulous developer. It was Patton who had Chadwick plant the larvae in her cane field so that after the sale, the land would be declared commercially inviable as a plantation. Patton could then buy it for next to nothing and turn it into a site for hotels and high rises.
Eager to find the spot where the larvae were planted, McGarrett has his newspaper and radio cronies issue bulletins saying that the larvae threat is over. In a panic, Patton races to the site and discovers that
At the close, Mrs. Holbrook learns that Patton, Chadwick and Vadney are headed for jail and that her plantation is economically viable. She was never in danger of bankruptcy.