Act of Oblivion by Robert Harris
In 1660 a group of men were hanged until they were not quite dead. They were taken down, alive, and then castrated. Their entrails were pulled out in great, looping coils and burned in front of them. Their hearts were plucked from their chests. Finally, they were beheaded and cut into quarters. Their crime? They killed a king.
The newly restored monarch, Charles II, was pragmatic. He issued a blanket pardon known as the Act of Oblivion to those who fought for Parliament in the Civil Wars, but it came with one principal exception. Those men responsible for killing his father were to be hunted down and executed in the grisly manner reserved for traitors.