From David Lubar himself: Ryan and Taylor are twins, but they have nothing in common. Ryan fails at everything he tries. Taylor tries to be perfect. Then Ryan stumbles across alien disks that let him change into legendary figures from the past. Suddenly, both their lives start to change in unexpected ways.
And to add to what Mr. Lubar says: Ryan is a boy and Taylor is a girl and they're about to have a chance to be heroes the easy way. They're both in the eighth grade.