The Helios Conspiracy - Spectre Series, #7

In Book 7 of the Spectre Series, Spectre once again finds himself in a fight for his life, but this time, he's not alone. After saving his old teammates in Iraq one last time, Major Cal "Spectre" Martin has hung up his G-suit in favor of a new career as an airline pilot. But when Spectre learns that one of his friends has been killed in what authorities are calling a gas explosion, Spectre sets off on an investigation that places him right in the middle of an international conspiracy that aims to bring the Western world to its knees.
With the help of a few old friends, Spectre must uncover the truth, clear his name, and stop a group of rogue billionaires from launching their deadly project codenamed HELIOS.