The Devil's Engine Series by Alexander Gordon Smith

There is a machine from the darkest parts of history, concealed in an impossible location, that can make any wish come true, and the only price you have to pay is your soul. Known as the Devil's Engine, this device powers a brutal war between good and evil that will decide the fate of every living thing on Earth... moreThere is a machine from the darkest parts of history, concealed in an impossible location, that can make any wish come true, and the only price you have to pay is your soul. Known as the Devil's Engine, this device powers a brutal war between good and evil that will decide the fate of every living thing on Earth. When a 16-year-old asthmatic kid named Marlow Green unwittingly rescues an ass-kicking secret soldier from a demonic attack in the middle of his Staten Island neighborhood, he finds himself following her into a centuries-old conflict between a group of mysterious protectors and the legions of the Devil himself. Faced with superpowers, monsters, machine guns, and a lot worse, Marlow knows it's going to be a breathless ride and not just because he's lost his inhaler along the way. less

In Hellraisers, he made a demonic deal. Now it's time to pay the price. Thrown into a relentless war against the forces of darkness, fifteen-year-old Marlow Green and his squad of secret soldiers must fight for control of the Devil's Engines--ancient, infernal machines that can make any wish come true, as long as you are willing to put your life on the line... moreIn Hellraisers, he made a demonic deal. Now it's time to pay the price. Thrown into a relentless war against the forces of darkness, fifteen-year-old Marlow Green and his squad of secret soldiers must fight for control of the Devil's Engines--ancient, infernal machines that can make any wish come true, as long as you are willing to put your life on the line. But after a monstrous betrayal, Marlow, Pan and the other Hellraisers find themselves on the run from an enemy with horrific powers and limitless resources--an enemy that wants them dead at all costs. Failure doesn't just mean a fate worse than death for Marlow, it means the total annihilation of the world. And when all looks lost and the stakes couldn't be higher, just how far is he willing to go?The thrilling sequel to The Devil's Engine: Hellraisers is perfect for teen readers who like action-packed, high-stakes novels. less

After Marlow makes a deal with the Devil to get himself and Pan released from Hell, war breaks out and the friends have only each other, and hope, to combat demonic creatures and monsters.