While rescuing a girl from an abductor that turns out to be her father (and indeed the one person the girl wants to be with), Batgirl realize that David Cain really is her father.
David Cain returns to Blackgate Penitentiary after giving Cassandra a gift. Upon opening it Cass discovers it's a small assassin knife. She takes it to Barbara Gordon and Batman, who both agree it's a nice knife but have no idea why Cain gave it to her. While with Barbara a call comes in about a kidnapping.
Jill is a little girl who is also a talented artist, and she has been abducted by David Sullivan. Her mother is her agent and cares more about the gallery opening then her daughter well being. Batgirl notes this and waits outside till David shows up.
When he does Batgirl follows him home where Jill is being kept. She confronts him but David and Jill make an escape via a hang glider and some insane stunts. Even with these Batgirl is able to catch them but when she tries to rescue Jill, Jill doesn't want to leave David's side.
That is when Batgirl realizes that David is Jill's father and that Cain is her father. David pleads to let him and Jill disappear but Batgirl can't do that and lets David get captured. Jill is returned to her unloving mother and Cass returns home to break the knife that her father gave to her.