The sixth and penultimate book in the New York Times bestselling I Am Number Four series! For years the Garde have fought the Mogadorians in secret. Now all of that has changed. The invasion has begun. John is on the front lines of the fight in New York City. And just as the odds seem stacked against him, his best friend, Sam, a human, inexplicably develops a Legacy-and Sam isn't the only one. While the pair try to track down Five and Nine amid the chaos, they encounter another teen who can wield abilities that were once only meant for the Garde. Whether she is a friend or a foe, however, remains to be seen. Meanwhile, Six, Marina, and Adam are trapped in Mexico. They fought their way into the Sanctuary and were able to awaken the power hidden within, but their preceding battle has left them without any way to reach the others. The Mogs are returning in full force, and it will take a miracle to escape. The Garde are stretched thin, fighting this war on many fronts. The only chance they have is to take out the Mogadorian leader once and for all-but his fate is now irrevocably tied with Ella's. They can't destroy one without the other. But if the Garde can't find another way to stop the Mogs, humanity will suffer the same fate as the Loric: annihilation.