'After their adventures in Transylvania, Anna and Max just want to stay out of trouble – but trouble has other plans. The Professor’s taken them to the cold and foggy fields of England, where a new mystery is afoot. A small boy has disappeared near a strange and mysterious river, lost without a trace.

'Armed with her magical white knife, Anna is determined to crack the case, boldly leading Max into danger and darkness. With memories of the fairy world still haunting her dreams, Anna feels sure that another monster is behind the boy’s disappearance. But when the sinister secret of the river is finally revealed, will the siblings be able to save the missing boy – and themselves?'

Source: Publisher's blurb.