Retired film star Shara Weston lives alone on her island in the South Pacific, recovering from the tragic death of her lover four years ago. She is somewhat surprised to see a man fall from the sky into the water, and when she goes to help him, she discovers that he is rather unusual - not only because he dropped from the sky, but other things happen that seem a bit off. For example, he recovers very quickly, his clothes seem to change magically, and he has an obsession with salt.

Fairly soon, Cade Archer tells Shara that he is an alien and needs the volcano on her island to create a portal to his home world to transfer salt, something that is lacking on his world and an unjust hierarchy is in place which rations salt only to special people, "The Firsts." Cade's own brother Jamal is a First and is trying to prevent Cade's mission to find three special machines scattered around the planet which are needed to make the portal. Shara's friend Jules has visions which usually come true, and one of her visions predicted just this - and that Cade's actions would destroy the world. Shara decides to appear to help him and then, when convenient, scupper his plans.

The action moves from Shara's island of Haven to Hawaii and then mainland USA. Various other people are involved in the plot, including Jules, a security expert, a reporter and a vulcanologist. Shara and Cade face dangers all around, including escaping a burning building, an airplane crash, being stranded in the desert, being held at gunpoint, and being controlled by the mind of Jamal. They seem to shrug all this off with remarkable aplomb, and this especially goes for Teresa Alverez, the security expert who seems to recover almost overnight from being tortured by Jamal and left for dead. Although obviously parts of Island Heat have to be beyond belief (being about aliens), it's actually harder to swallow the actions of the humans in this story.

The romance aspect is less important to the story than the earth-destroying plot ,and in some ways it's a romance born of nearness and mutual appreciation rather than anything else. Cade worries as he starts to gain powers previously reserved only for the Firsts, including mind control, which he uses on Shara occasionally. She seems remarkably phlegmatic about it, apparently glossing over any future problems, and they are also both amazingly forgiving of some of the dodgy and untrustworthy things they do to each other. That's my main criticism with the book; the action is okay, the plot is okay, but the alien aspect just doesn't work. There's no world-building as one would expect, and the aliens aren't human yet seem to have no problems having sex with humans and even making babies with them. Cade seems to need only minimal adjustment to this alternative world, and although we learn that his culture sees relationships with women very differently than on Earth, he is able to commit to an Earth-type relationship within a week. It's okay to suspend disbelief when reading this genre of novel, but there's a little too much of that in Island Heat.