The First Rule by Robert Crais
The team thought that Frank Meyer had got out of the 'life' safely. He had put an end to his mercenary days, turned over a new leaf and settled down with his wife and children. It had been a hard decision but, encouraged by his boss and friend Joe Pike, he had walked away. But ten years later, a group of armed men break into his Los Angeles home and brutally gun him and his family down. It's a vicious, cold and professional job. The crew leave no trace behind except the bodies. But they have made one catastrophic, and almost certainly terminal, mistake - Joe Pike. Because Pike is now determined to hunt down and eliminate everyone involved in the attack one by one. And it doesn't matter that, as he starts to investigate, he discovers that this group of criminals are bigger and more well-organised than he ever could have imagined - part of sprawling gang of east European mafia. None of that matters, they are going down anyway.