"Franky.. I'm a plumber."
Alan Doyle is the father of inmate Franky Doyle, who abandoned her when she was just a kid. He works as a plumber. He appears in season 1 when he tries to reconcile with Franky who instead rejects him, blaming him of having left her alone to face her life with her abusive mother.
He appears again in the first episode of season 4, when he peeks at his daughter who is out on parole, though his identity stays secret; it will be revealed in the following episode, when he runs after Franky two times letting her know that she has a three-year-old sister.
In episode 5x09, Franky convinces him to help her escape after he visits her in prison where he reluctantly agrees to help he uses his skills as a plumber to get Franky the stuff she needs through the prison plumbing, when the route to the shower is blocked by Joan Ferguson having a shower he uses the plans to switch routes and goes into the kitchen.
In episode 6x03, after Franky's charges are dropped, he greets and comes back to his daughter in a park in a happy farewell scene.