Attack of the Evil Elvises (Hardcover, Turtleback School & Library ed.)

After thier spaceship is taken by the Great Ones, Ploo, Klatu, and Lek return to Las Vegas. There they discover an infestation of Elvis
impersonators, in town for a convention. Klatu, Lek, and Ploo are sure the odd-looking humans are up to no good, and it turns out that they're right . . . for once. These are no ordinary Elvises--they are evil aliens from outer space in disguise with nefarious plans to take over Earth!