The year 1662: Restoration England. Cromwell is dead, and King Charles II has reclaimed the throne after years of civil war. It is a time of divided allegiances, intrigue, and outright treachery. With rebellion stirring in the Scottish Isles, the hard-pressed sovereign needs officers he can trust to sail north and defuse this new threat.

Matthew Quinton is such a man-the second son of a noble royalist family, he is loyal, if inexperienced. Having sunk the first ship he commanded off the coast of Ireland, Matthew is determined to complete his second mission without loss of life or honor. But aboard His Majesty's Ship the Jupiter, the young "gentleman captain" is faced with a resentful crew and has but few on whom he can rely: Kit Farrell, an illiterate commoner with vast seafaring experience, and Phineas Musk, a roguish but steadfast family retainer. As they approach the wild coast of Scotland, Matthew begins to learn the ropes and win the respect of his fellow officers and sailors.

But he has other worries on this crucial mission: a suspicion that the previous captain of the Jupiter was murdered, a feeling that several among his crew have something to hide, and a growing conviction that betrayal lies closer to home than he had thought.