Haney and Cardy bring back the Mad Mod as the Teen Titans go to England in issue 17 (Sept/Oct 68).
Robin accidentally gets locked in the Tower of London right at the top of the story, so Aqualad, Wonder Girl and Kid Flash have to deal with the Mad Mod themselves after he steals the Queen's sceptre.
Each one gets a good chance at retrieving the sceptre, thanks to the Mod's tendency to talk about his hiding places, and it takes them around the map of the country. But each of the three heroes wind up getting knocked out by the Mad Mod and his men.
As the story goes on, Kid Flash, Aqualad and Wonder Girl realize that they are feeling much weaker, and do not seem to be able to use their powers fully.
Eventually they determine that their costumes have been gimmicked by the Mad Mod to suppress half their powers. They change into fresh outifts, and have a final battle, during which Aqualad saves the villainous designer from drowning.
The conclusion is fun. They finally free Robin from the Tower, and he throws a big fit, totally unaware of the events of the story, and not understanding why he felt too weak to free himself.
The Mad Mod is not seen again until the Teen Titans series from the late 90s, when he has reformed.