The Covenant. The Magician's Granddaughter, #4

Immie Whitfield and her circle have mapped the Collector network, destroyed four supernatural nodes across three continents, and built the legal case that will bring the organisation down. Now they know what is left: not a building, not a ledger, not an archive. A manufactured thin place in the west of Ireland, built a hundred and fifty years ago from a covenant that was never supposed to be sealed - holding the original agreement, the true version, the one that proves the Collectors were wrong from the very beginning.
The only person alive who knows where it is, and how it was built, is Adelaide. She is eighty-three. She built it at sixteen. She has been waiting sixty-seven years for the chance to help undo it. But first, she has to earn a seat at the Thomas Street kitchen table. The Covenant is the conclusion of The Magician's Granddaughter - a four book series about young women with special gifts, one ancient Irishman, a circle of gifted people who changed everything, and the single most important thing in the world: paying full attention.
They go to Sydney. Then London. Then home. Then Ireland. Tea first.