The way I see it, the primary plot entails the relationship of the con man, Roy, with his daughter. The long con job he pulls with his partner, Frank, is a subplot.

Why?

Because, for one thing, the long con is Frank’s idea — not Roy’s. Roy initially refuses to do it and agrees only because he’s in an agreeable mood after seeing his daughter.? His partner is the one who takes the initiative on the long con plot thread — not Roy. Frank is in the driver’s seat; Roy is going along for the ride.

Come to find out, his partner is in the driver’s seat of the con job in more ways than one. (Spoiler alert!)

The big reveal is that the real mark is Roy.? Frank is out to manipulate him out of his considerable stash of cash.? And that his daughter is not his daughter, but the hook used to reel Roy into his partner’s con.

(The movie is a con job on the audience as well. We don’t find out about it before the protagonist does. )

No matter. A logline is a description of what the protagonist knows or believes at the time he commits to an objective goal — not what he discovers in the 3rd Act.? At the end of Act 1, Roy believes his daughter is the real deal and everything he does is motivated by that belief.

One other point: there is a denouement, a scene of closure to the relationship between the protagonist and his “daughter” — they meet a year later. It’s not a joyous reunion, but it is a resolution of their relationship.? In contrast, there is no closure, no resolution with his partner, the mastermind of the con against Roy. He just disappears with his cut of the loot.