"I called on darkness… midnight darkness…" At the end of the 18th century, the poet William Wordsworth rambled, in a strange visionary haze, from Salisbury Plain up into the Wye Valley. The epic walk changed his life. More than 200 years later, Oxford student David Vaynor followed the same secluded route and still can’t explain what happened to him there. Now he’s back, as a police detective investigating a suspicious death and finding that, in this place of awesome cliffs and chasms, there are crimes the police can’t deal with. Meanwhile, Merrily Watkins, diocesan exorcist for Hereford, is being warned that in-depth investigation is not part of her job – a job she may not be holding down for much longer. At the start of the national lockdown caused by the threatening pandemic, she’ll be risking her future to help Vaynor uncover the secrets of England and Wales’s most revered river. For behind the scenic beauty are elements that, as Wordsworth put it, ‘promote ill purposes and flatter foul desires.’