At the dawn of their adolescence, on the eve of the summer solstice, four young girls—Helena, Leonie, Niamh and Elle—took the oath to join Her Majesty's Royal Coven, established by Queen Elizabeth I as a covert government department. Now, decades later, the witch community is still reeling from a civil war and Helena is the reigning High Priestess of the organization. Yet Helena is the only one of her friend group still enmeshed in the stale bureaucracy of HMRC. Elle is trying to pretend she's a normal housewife, and Niamh has become a country vet, using her powers to heal sick animals. In what Helena perceives as the deepest betrayal, Leonie has defected to start her own more inclusive and intersectional coven, Diaspora. And now Helena has a bigger problem. A young warlock of extraordinary capabilities has been captured by authorities and seems to threaten the very existence of HMRC. With conflicting beliefs over the best course of action, the four friends must decide where their loyalties lie: with preserving tradition, or doing what is right.