Wild's End: The Enemy Within — Dan Abnett

The invasion of Earth was just the beginning for this unlikely team of heroes.

As Clive, Susan, Fawkes, and the other survivors of the alien invasion of Lower Crowchurch try to cope with what just happened to their small town, the military arrives in an attempt to cover up the "incident." Town residents are immediately detained, questioned, and treated with suspicion. Are they alien spies, collaborators, sympathizers? Clive and the rest will need to escape imprisonment if they're to get the word out and warn the rest of the world in case the aliens return.