The Legion gets drawn into a war between gangs on Earth in Adventure 374 (Nov 68), a Jim Shooter tale that introduces Leland McCauley, a business rival of RJ Brande.
The Legionnaires get attacked at a variety of locations, and the five who remain, Ultra Boy, Supergirl, Element Lad, Dream Girl and Matter-Eater Lad, are teleported by the leader of a gang called Scorpius, who informs them that their teammates will be killed unless the five take down the members of a rival gang, Taurus.
The Taurus Gang are a kind of half-assed Fatal Five. None would appear again after this story, except for Black Mace. For many years though, Legion fans would theorize a connection between Quanto and the similarly costumed Reflecto from the Adult Legion story.
The Legionnaries fight them in disguise, so out of costume, but the Substitute Legion try to break up the fight, and Polar Boy recognizes them.
The current chief of the Science Police, Zoltorius, is the actual leader of the Taurus Gang, but disguises himself as RJ Brande, and tries to frame rival millionaire Leland McCauley as being the head of Scorpius. This is kind of pointless as far as the story is concerned, but Leland McCauley will appear again in a number of stories.
Dream Girl infiltrates the Taurus Gang by posing as Mystelor, and Quanto reforms on his own, leaving the gang, but it’s the Subs who get to swoop in and save the day at the end, their last appearance before the end of the Legion’s run in Adventure.