Batman #567, p. 6: First Page Appearance David Cain (3rd Pg. App. Cass Cain)

Fate brings together Cassandra Cain and her abusive father, the assassin David Cain.

Upon exiting the makeshift offices of the GCPD in the post-apocalyptic No Man's Land-era Gotham City, Cassandra spots a familiar face, and stricken, drops the papers she's to deliver as courier. David Cain turns to look, but Cassandra cannily slips out of sight.

In subsequent pages, she stalks him as he picks out a sniper nest from which he intends to pick off Commissioner Gordon.

Cassandra knows from personal experience the threat he poses. Raised by him in silence so she could internalize body language as her first language, she was subjected to nothing short of extreme abuse in an effort to make her a perfect weapon. It's revealed later in the Batgirl series when Robin sees the scars on her back that her father shot her as part of her training. When asked how the scars could be so large, she replies "I grew."

Having fled his "care" in childhood after regretting her first kill, she wanders until she comes to Gotham City. When her father shows up, she knows he must be up to no good, and only she can successfully intervene...