Fantastic Four #28 - (as reprinted in Giant-Size Fantastic Four #4) A prototypical crossover tale. The Puppet Master takes control of Professor X and his mental powers, in turn using them to control the X-Men to attack the Fantastic Four and whatnot. Eventually, Beast breaks the control and the differences are more or less resolved. Great art by Kirby as per usual, middling story by Stan Lee , and about two ridiculous editorial goofs by Lee. Worth reading regardless.