No Man an Island by Gavin Williams

Eight friends gather for a reunion vacation, but go missing after a hurricane strikes along their plane’s flight path.  While friends and family mourn their loss when the crashed plane is found, the impossible happens: they appear in public claiming to have been in a cave in the mountains.  Missing for months, they have no memory of the interval. 

What happened on that mountain, and the events that follow, will test their friendship, their faith, and the world.  It leads to apocalyptic battles, angels and demons, and a confrontation with the devil himself.