The Teen Titans face the first masked opponent in their own book as Haney and Cardy pit the team against the Ant in Teen Titans 5 (Sept/Oct 66).
At the top of the story Robin, Kid Flash, Aqualad and Wonder Girl are hanging out in Titans Lair when they receive a letter from Speedy, referencing the events in the previous issue. Then they get asked to look into the possible return to crime of a boy who had been sentenced to Camp Lacklock, a progressive institution for juvenile offenders. Eddie Whit has more strength and agility than most kids his age, but nothing super human. He had done his time, and been released, and was now taking care of his younger brother.
The brother insists that Eddie has not returned to crime, but the Titans find his Ant costume, and wind up chasing him, and fail to stop him. This failure puts Camp Lacklock itself in danger, threatening its reputation, and dispiriting the kids who are currently there.
In the end, it turns out that Eddie has been manipulated into becoming the Ant again, by hoods who have tricked Eddie into thinking his younger brother has also turned to crime, and are blackmailing him about it. A good, solid story, with all the fun patter and great art.