After a decade as a back-up feature in Action Comics, Supergirl moves to take the lead in Adventure Comics, with issue 381 (June 1969). Cary Bates and Win Morimter take the reins on this tale, which has Linda visiting her cousin Superman in Metropolis.
She encounters a group of female thieves, one of whom is a friend from Stanhope College. After being captured, the women have no memory of their crimes. Supergirl connects them to a “sleuth school,” and decides to enter it undercover to investigate.
The top student is a woman named Barbour, who has her own secret agenda, but the man running the school, Jonathan Maxom, is unaware of that, and pits her and Linda against each other.
It turns out Barbour is Batgirl in disguise, who saves Supergirl when Maxom tries to kill her with kryptonite.
Not a bad story, mediocre art though.