Over a decade before Margaret Thatcher swept to power, another woman was running Britain from 10 Downing Street: Marcia Williams was the first ever female political adviser to a Prime Minister and was said to have a powerful grip on her boss. A brilliant tactician, Marcia masterminded Labour Prime Minister Harold Wilson's multiple election victories. But misogyny, jealousy, a shocking private life and accusations of money-grubbing and bribery all contributed to her reputation as a public nuisance. There is no doubt Marcia was outspoken, forthright and, by contemporary standards, deeply unconventional. But her critics failed to understand her unbreakable partnership with Wilson – they were politically wedded to each other and equal contributors to his success. In this fascinating biography, updated with new insight regarding Wilson's Downing Street affair with Janet Hewlett-Davies, Linda McDougall seeks to rescue Marcia from previously dismissive verdicts, suggesting a more nuanced perspective and restoring this trailblazing pioneer to her rightful place in British political history.