The Harpers (LL Watkin Stories, #2)

The Lady of the Keep did not return to her people in the spring. The Lord reports that she is ill, too ill to even write.
There is an heir, or so the Lord claims at court, but no one has ever seen him. No one brave enough to tell the tale, anyway.
The Lord commands dangerous magics and keeps many secrets, but his Lady's people are powerful too and they are coming for answers.