my name is johnny lawrence, i am a karate sensei and all i know is that i have a son named robby who hates me
you lived with your mom and step father, you knew really knew your real dad. your brother robby would tell bad stories about him so you never thought about visiting him.
that is until robby gets sent to juvie and your mom is never home, you can't help but think about your dad.
so you grab a backpack, look in your moms things and find his name and address and make your way to visit him. (he doesn't know you exist)