It is only the seventh episode of the first series and it's the old identical double story.
Father Dowling has a lookalike in the family that he has never mentioned before. It is not a twin but an identical half brother.
Blane Dowling did not follow a righteous path, instead he has been causing trouble for Father Dowling and the good Father has had to pick up the tab. Blane even insulted housekeeper Marie and she is leaving not realising it was not Father Dowling.
It is all part of a cunning plan to steal a valuable diamond. Blane knows Father Dowling will interfere. When the time is right Blane plans to pick the diamond under the noses of the police.
It is really bad stuff, a load of drivel. Just imagine how bad the rejected scripts were if this was greenlit for production.