Being king can be a lonely business. Perhaps the less suited a person is to rule, the more urgently they feel the need for a companion, a favourite, who will ease their worries and provide their pleasures. James I of England was just such a monarch. Although he had an unshakeable faith in his right to rule, he required distraction from the heavy burden of state. Scholarship, including musing on the divine right of kings, was one of these escape routes; hunting and drunkenness, too; but his true solace, for nearly 10 years, was his beloved bedfellow, George Villiers, whom he raised from humble origins to become Duke of Buckingham.

Buckingham has been relatively overlooked because his identity-bending role as James’s “sweet child and wife” rendered him somehow suspect. A man whose skills included dancing like a dream and looking marvellous on a horse was seen as less worthy of study than a minister of state, despite the decade-long role Buckingham would grow into as co-architect and implementer of Stuart policy. The fact that the issues that would tear the country apart when the civil wars began 14 years later had their roots in these policies only adds to his importance. This fabulous biography is long overdue.

A one-off in English history, he must have been quite something in person. In portrait after portrait, by Van Dyck, Rubens and a crowd of other masters, his grey-blue gaze coolly invites us to admire his resplendence: the luscious dark curls; the milk-white skin; the fine, strong legs; the heavy ropes of pearls. It is a truism that Buckingham rose on the crest of the king’s lust, but, as Lucy Hughes-Hallett demonstrates, he was also propelled by charm, modesty, adaptability and a prodigious work ethic – especially if you add receiving passionate public embraces and writing adorable love letters to the business of government.

Like The Pike (her 2013 biography of Italian poet Gabriele d’Annunzio), The Scapegoat is a doorstopper, at once detailed and discursive. Hughes‑Hallett is as concerned with hunting and horsemanship or garden design as she is with “peace and war, Parliament and despotism”. An account of Buckingham and Prince Charles’s melodramatic escapade to Spain in

Historians need anthropological as well as psychological skills, and these Hughes-Hallett possesses in abundance, along with an easy, wry wit. Guiding us through Buckingham’s “entrancingly strange” netherworld, she strikes a delicate balance between exploring the attitudes of 17th-century society and keeping her feet firmly in the present day. Jacobean people believed in ghosts, witches and magic, but not for an instant does Hughes-Hallett patronise their faith; for example, when probing Buckingham’s fateful involvement with John Lambe, a self-declared doctor and wizard. Buckingham initially consulted Lambe, whom he called “my devil”, about his “mad” – probably bipolar – brother, but retained him as an adviser, perhaps to use his love potion-making skills or his curses, practices for which Lambe had spent time in prison.

Apart from James, Buckingham is only known to have desired women. It seems safe to assume that his love for James sprang from ambition, but Hughes-Hallett makes a good case for deep affection on both sides. Buckingham supplied James with the cosy family life he craved: James evidently adored Buckingham’s mother, wife and children, and Buckingham restored the neglected bond between James and his shy, stubborn son, the future Charles I.

Although Buckingham was portrayed as Adonis and Mercury in paintings commissioned by Gerbier, the mythological figure he most resembles is Icarus, the boy whose dreams outstrip his capabilities. His assassination at just 36 feels as inevitable as it was bloody and chaotic. Even at the time, contemporaries recognised that removing Buckingham, by then the scapegoat of the title, would do little to improve the increasingly unpopular regime he’d been at the heart of. “It is said at court there is none now to impute our faults unto,” wrote one. The discord and frustration that would lead to revolution were already out of the bottle.