BOOK REVIEW / Sailor who knew how to serve two masters: Cromwell's Earl: A Life of Edward Mountagu, Richard Ollard; HarperCollins, pounds 20

IT IS widely believed that the restoration of Charles II in 1660 saw the total rout of the republicans and the triumphant return of the Royalists to power and office. As old Cavaliers were the first to complain, however, this is too simple. Edward Mountagu exemplifies that group of grandees who made a successful transfer from office under Cromwell to the Restoration court.

The son of a Puritan Royalist, Edward joined the Parliamentary army and rose to a command in the New Model Army before he was 20. An admirer and intimate of Cromwell, the Protector appointed him joint General at Sea with the indefatigable Blake in 1656, in which post he seized rich prizes from the Spanish off Cadiz. At home, Cromwell granted Mountagu lodgings at court and secured him a seat in Parliament, where he led the party that offered the Protector the crown.

In the period of uncertainty that followed Oliver's death, when army factions vied for control, Mountagu laid low. But as Monck marched to London, Mountagu - as Clarendon had predicted - added his support to the restoration of the Stuarts. Charles II went ashore in England on Mountagu's barge and soon rewarded him with an earldom, the Garter and a place in his Council.

The navy presented slightly more of a problem, since the king's brother, James, held the admiral's post and was determined to command at sea in fact as well as in name. As General at Sea, Sandwich promoted Cromwell's old policy of gaining a base in the Mediterranean, and secured Tangier.

But he never saw eye to eye with the Duke of York, whose faction, always looking to undermine him, brought a charge of corruption that threatened his disgrace and impeachment. He eventually left his command to take up an embassy in Madrid, and then Lisbon, where he resided from 1666 to 1668, recording in a fascinating journal the topographical and human characteristics of the land.

But in the new circumstances that followed the fall of his friend Clarendon, Sandwich found himself outside the inner ring of power. Charles II's secret treaty of Dover, about which he was not consulted and of which he did not approve, led to the war against the Dutch in which Sandwich met the death he had uncannily predicted.

Ollard is right to claim that Sandwich has been denied the high place in history to which he is entitled. An example of his age, he combined military command with a knowledge of mathematics and astronomy, a love of art and sculpture, skill in observation and drawing and a taste for building and gardening. His politics and beliefs, however, remain an enigma. Though 'not cut out to be a politician', Sandwich stayed afloat in some turbulent political seas from the 1640s to the 1670s.

His friendships with Cromwell, Clarendon, Milton and Evelyn also raise questions about the nature of his pragmatism and principles that would be worth exploring further. His religion, not discussed here, is even more mysterious: the son of a strict Puritan father, Sandwich lived in a debauched court, and at Lisbon observed the burning of heretics without comment - even to the private pages of his journal.

The political and ideological world in which Sandwich moved and manoeuvred sometimes remains shadowy and indistinct. But Ollard draws a fascinating and elegant portrait of the man who was both Cromwell's and Charles II's earl. Invaluably, he thus moves him from obscurity to the historical foreground where he belongs.