At End of Day is the story of an unholy alliance between two members of the Boston mob and a select group of FBI agents whose careers have been made successful through information these mobsters have provided about their Mafia counterparts. The FBI, in turn, has protected these men from prosecution which has allowed them to even commit murder with impunity (though this is "against the rules"). This tale is all the more interesting because it is based on a true story.
It is a shame that this is the last Higgins book we will have. He died as it was going to press. On the positive side, he wrote so many books during his career that fans of his style should have no trouble finding something to satisfy that acquired taste.