This book was okay on suspense but there were aspects of the plot that didn't make sense. Basically a meteor falls out of the sky and impacts near Denver, the blast effect destroying much of the city. Soon thereafter, the dust and debris swirling in the sky turns the weather freezing and some kind of alien microbe reanimates and mutates all the dead.
But the author never addresses the one nagging question that kept occurring to me all throughout the story-- namely, is this something localized to the Denver/central Colorado region or is it worldwide? From the description of the impact event, there's no reason to believe cities on the other side of the planet would even be affected. And even if the alien microbe rained down everywhere, only Denver had millions of dead bodies for it to reanimate because only Denver actually got hit by the meteor.
And what's more, it never occurs to any of the characters in the story to even wonder if what's happening to them is happening everywhere. They never think to try and get in a car and just drive east until they find other people. They never think that maybe the National Guard or the Army from outside the blast zone might show up at some point. They never speculate amongst themselves about any of it. It's like they just all assumed that since Denver was destroyed, they must be the last seven people left alive on the planet.
It was a very frustrating read because it seemed like the author was intentionally ignoring a key plot point, perhaps because he didn't have a way of adequately explaining or resolving it and figured that if he didn't mention it (through his characters), the reader hopefully wouldn't notice.