The Secret of the Bloodred Key by: David Farr (Book 2)

In this installment, siblings Rachel and Robert — who in the previous book defeated the tyrant Charles Malstain — believe their troubles are over. But after Robert becomes distracted by new friends and their father struggles with grief after their mother’s death, Rachel learns she has been entrusted with a mysterious “blood‑red key” — a key that grants access to the Hinterland, a haunting otherworld where the dead dwell.