The Siege of Trencher's Farm by Gordon Williams (Paperback / softback, 2011)

American professor George Magruder, his wife Louise and their daughter rent an old, isolated house kwn as Trencher's Farm in Cornwall, so George can finish writing his book. When George accidentally runs over a convicted child killer on the loose from a mental asylum, he confronts the brutal locals and sets in train a series of violent events that threaten his very survival and that of his family.