Another neat and nasty occult fright--from the reliable British author whose mostly paperback horror novels (The Manitou, Tengu, Mirror, etc.) counterpoint his more massive and mostly hard-cover potboilers (Rich, Lady of Fortune, Headlines, etc.) Here, a band of the criminally insane terrorizes the greater Milwaukee area. Not just any criminally insane, though; to Masterton's credit, he's dreamed up a fresh horror premise: that his villains, using druidic lore, can live on within earth and stone--through which they can ""swim."" So the novel bulges with scenes of Masterton's crazies--escapees from the Oaks, a rambling, deserted asylum in rural Wisconsin--channeling through the ground like demented moles, then reaching up and dragging down their victims (who, unprotected by druidic lore, are usually grated like Parmesan against the earth). Before all this gory gusto, though, Masterton offers a spooky setup, beginning when auto-repair entrepreneur Jack Reed comes upon the Oaks and feels compelled to buy it. When he revisits the Oaks with son Randy, the boy is pulled into the asylum's walls by unseen hands. After some sleuthing--bookworming, tracking down old witnesses, taking on a college prof as partner--Jack learns the Oaks' secret: decades earlier, it shut down overnight when all its inmates suddenly vanished; led by a druidic student/inmate/ferocity, Quintus Miller, the crazies had vanished into the walls and grounds--where they remain trapped, prisoners of a priest's blessing. So the crazies offer Jack a trade: his son for their freedom. Jack goes for it--and all hell breaks loose, including his own terrifying swim through the earth, until the surprisingly sour finale. Superior pulp, Masterton's best since The Manitou, full of energy and surprises enough to forgive the author's by-the-book characters and merely serviceable prose.