Who was the shocked man at the end of the film? (Spoilers)

I caught the beginning and end of this movie on television yesterday. Unfortunately I had to go out for a while and missed a lot of what happened in the middle. If someone who has seen the movie could answer this question, I would appreciate it.

At the end of the film, Adam looks up and sees Carver at the top of the stairs watching him. Another man comes up beside Carver, sees Catherine, and tries to rush down the steps - but Carver holds him back and then leads him away. Who was that man and what was his relationship with Catherine?

Thank you!