Teen Titans #14

Teen Titans #14 (On Sale: January 23, 1968) has a very nice Nick Cardy cover, as they slowly age the Titans and make them a lot more serious (at least on the covers).

"Requiem for a Titan" is by Bob Haney and Nick Cardy. The Gargoyle, a former Teen Titans foe who claims he was unjustly imprisoned by the team, sows the seeds of doubt in the minds of all but Robin, enabling him to banish them to the dimension of Limbo by means of his mystic ring. In Limbo, Kid Flash, Aqualad, and Wonder Girl become phantom giants under the Gargoyle's control and help him to battle Robin. Finally, Robin surrenders and allows himself to be transported to Limbo, so that he can fight the Gargoyle and his thralls on their home ground. Smashing the Gargoyle's ring traps the villain in the extradimensional realm, and restores Robin and his teammates to Earth and normalcy. Reprinted in Showcase Presents: Teen Titans Vol. 1 TPB.

Edited by George Kasdan.