But two songs do not a great album make, nor do they pose a sufficient answer to the challenge the Backstreet Boys presented at the start. The Boys once had an urgent message to deliver to the world: the sensation of hovering on a threshold, the manic bliss of potential energy beginning to explode. But someone dropped the bomp, and overnight the Backstreet Boys are becoming a revival act, riding on the juice they generated three years ago. They seem doomed to hover in the historical ether as perfect vessels of pure potential. And that would be tragical.