When Gorilla Grodd takes control over Titano, the giant ape, the only person who seems to be able to override his control is the medical worker who nurse him as a chimp. She's now known as Harley Quinn.
It is night time in the streets of Metropolis and Gorilla Grodd is on the rampage accompanied by an inexplicably huge chimpanzee called Titano. Grodd sits on top of the chimp inside a compartment with a canopy, and it is evident that he controls the huge animal against its will through a helmet on his head. Stargirl appears and protects civilians from cars that are hurtling through the air but she has to call on Superman for help. He soon arrives, but, equally inexplicably, Titano shoots kryptonite beams from its eyes at the behest of Grodd and Superman crashes to the ground. Stargirl uses her rod to whisk him away to safety before he can be hit again. Superman flies away to find a solution to the beams, leaving Stargirl to clear the streets.
The streets are already deserted and, to complicate matters, villainess Harley Quinn uses this as an opportunity to raid a jewellery store. As she helps herself to some diamonds, Stargirl smashes through the door, expelled from a disturbance outside. The latter is unsure of which problem to deal with first but then decides to catch Harley in a force field. When Titano puts its hand through the door to find Stargirl, it grabs Harley instead and takes her outside where she greets Grodd, but he shows no interest. She then recognises Titano from some earlier time and when it was a lot smaller, but Grodd interrupts and the giant chimp hurls her away into the distance.
She is caught by Superman, now wearing a lead-lined suit, and he puts her down on a rooftop and flies to deal with Grodd. Harley relates to Stargirl that she knew Titano when she was studying animal psychology at S.T.A.R. Labs and was used to calm down the normal-sized chimp while it was being trained for a space flight. Later, while in space, it collided with a kryptonite meteorite and transformed into Titano.
Superman, no longer affected by the beams, becomes involved in an extended fight with Titano. He cannot break through the canopy to get at Grodd so he goes for a longer run up (to the North Pole) and, returning at speed, manages to crack it. Grodd responds by getting Titano to hurl a series of trucks which tear open Superman's protective suit, and then paralyzes him with the kryptonite beams. Stargirl, to save him, leaves Harley Quinn and hurls the trucks back at Titano, eventually breaking open the canopy and ejecting Grodd into the street. Titano, freed from control, takes the compartment off his head and attacks Grodd, hurling him through the air to land conveniently in the police wagon.
Titano is then assailed by police helicopters with orders to shoot to kill. It clambers over buildings to escape and picks up Harley Quinn before ascending to the top of the Daily Planet building. A recovered Superman intervenes to stop the helicopters and Stargirl brings an oversized teddy bear (an advertising prop?) to calm down Titano. Superman also stops Harley from escaping, and she is put into the wagon with Grodd where she offers psychological counselling to the self-doubting gorilla.
Appearing in "Harley Goes Ape!"