Night Shadows by Stephen L Brayton
Des Moines Homicide detective Harry Reznik and F.B.I. agent, Lori Campisi, have their hands more than a little full when they team up to investigate a series of gruesome murders.
With life throwing them one obstacle after another, the unlikely pair has no choice but to put their personal issues aside as they battle malevolent creatures from another dimension. With everything to lose, they have no one but each other to count on in a wicked game of survival.