The Beast of Baloddan by Andy Cutbill
Robert Twistleton, Bert to his friends, is an eleven-year-old boy whose family has run the Baloddan Hotel, a bleak Victorian edifice incongruously built on a windswept Cornish headland, for over a hundred years.
Bert is a quiet, unassuming boy who is all set to enjoy the uneventful summer holidays, until the day he discovers his grandmother has been sucked down the toilet and replaced with a slick of slime across the bathroom floor. SOMETHING has taken her.
Bert decides to investigate. With his friend Ruby he explores deep beneath the hotel, through underground tunnels, secret passages and hidden rooms. He discovers that people have been disappearing for years, and that matters will come to a head in only a few days' time at the total eclipse of the sun. Bert suspects that some of the locals know what's going on, although he isn't sure who. Could it be the shuffling shop keeper? Or the hook-nosed vicar? Or even his own grandfather?
Pieces of the puzzle are falling into place, but time is running out fast ...