Standalone by Paul Michael Anderson

They are killers. They are monsters. They are evil. They stalk through summer camps, abandoned hospitals, rundown schools, and isolated houses, hunting anyone foolish enough to visit these places, leaving behind carnage, terror, death, and destruction. Sometimes, there are survivors. Always, there is blood. And they do it to protect and preserve all of existence across the Multiverse. But now they are the ones being stalked and hunted, and life as we know it hangs in the balance unless they figure out a way to survive.