It continues in hot spots around the globe: Hawaii, where a secessionist movement is about to turn violent and the American army may be asked to fire on U.S. citizens; Washington, D.C., where the subway system becomes the site of a running gun battle; the Far East, where disrupted diplomatic negotiations jeopardize world peace; a rogue Russian submarine, circling the infant volcano.

Caught in the middle is Philip Mercer, a geologist and a one-time commando with shady contacts in all the right (or is it wrong?) places. When Mercer learns that the daughter of an old friend is being kept under armed guard in a local hospital, he vows to rescue her, not knowing that this is the first step in unraveling the fantastic secrets of Vulcan's Forge.