Mirasol has, after the fiery death of the last Master and Chalice, become the Chalice of her demesne, despite being a poor woman with a woodright and bees, despite holding her Chalice in honey. (Water usually, wine, cider perhaps, sometimes brine, milk is bad luck but possible, blood she has only heard of once, but never ever honey -- before this.) And the new Master, the brother of the dead one, has been summoned back from the priests of elemental fire, something no other priest has ever attempted. But he's of the right blood and having an out-blood Master has had horrific consequences in the past.
He burns her when they first meet. By accident, when he was bone-tired. But there was a case in the past where a Master was executed for harming his Chalice.
And when they are trying to weave together the earthlines to keep the land whole, and she is studying desperately to try to catch up, since she was dumped into the role with no apprenticeship, and the Master is trying to win over his people despite the -- transformations he's undergone -- why, the Overlord decides to dump an Heir on them. An outblood Heir, of course, they would not have tried this Master if there had been anyone else of the right blood to introduce. . . and Mirasol finds things going from bad to worse.
I was at first put off by the assigning of titles to the characters as part of the magic, which often presages a weak, schematic magic system. Not here, however; the magic works into the world-building and has further reaches which are suggested but not delineated, like any system too large to fit in a book. It helps that she's the demesne's Chalice, not the world's One True Chalice.