Shark Knights: Dead End — Eric Williams

A warrior race from another universe has sent their best soldier to Earth. His mission; destroy all opposition and enslave the world. Making matters worse, the alien has recruited the toughest villains on the planet to help him. Only the Shark Knights stand in their way. The team of adventurous super heroes has always prevailed over evil in the past. But they've never encountered a force so ruthless, or lethal. During the struggle, friendships are shattered, an underground predator rises up and a mysterious tournament invites anyone who dares to test their fate. Will the Knights be able to save the world, or have they reached a dead end? (This is the second book in the Shark Knights series)