From the back of the book:
It is 1963 in New York, and things have never been better for the Corleones. They've taken out their Mafia rivals, and legitimised the Family. Outside the fortified building owned by Michael Corleone, newly undisputed Boss of Bosses, a parade of people - among them former mob rivals and an emissary from the Mayor of New York - wait to ask the great man for favours.
Only one thing remains to be done. Traitorous former Corleone capo Nick Geraci has powerful friends and far too much to say, and needs to be brought in. But then everything changes. As fireworks explode over First Avenue, news arrives that Jimmy Shea, President of the United States and an old friend of the Corleone's, has been assassinated...
The title of this book is somewhat misleading. Sure Michael Corleone has a revenge of sorts but mainly, THE GODFATHER'S REVENGE focuses on the political side of mafia life and traitor to the Corleone regime in Nick Geraci.
Reading the back of the book is more spoiler than synopsis - the events detailed don't happen until the final third of the book and by then, the reader is well aware they are coming and what the likely outcome is.
I will say, that Tom Hagan, a crucial member and close friend of Don Corleone is well written. His part, along with Geraci's scenes make this book worth a read alone - unfortunately there isn't much more going for this book apart from that.