The Rise of the Demon by Nick Burgin
Eight years ago Jason's fiance, Leah, disappeared, abducted by an ancient demon. Since that day he's searched high and low for any evidence that the demon has resurfaced. Rose and Avril are on holiday in Portugal. Strange things are happening; violent dreams, depraved visions, dark thoughts. Then Avril vanishes, surely another victim of the demon. Together, with the help of an old friend, Jason joins forces with Rose to find the love of his life and stop the demon once and for all. From England to Portugal, Morocco to Turkmenistan, the friends will stop at nothing to end this nightmare.