Stranger at the door (2004)

Katherine "Kathy" is happily married to businessman Greg Norris and lives in his beautiful home with his about 18-year old daughter Tara. When suddenly a charming young man, who Tara first saw lurking around in the garden, turns up on their doorstep claiming he must be Jamie, the baby son she once gave up for adoption as a teenage mother on her parents' orders, the couple is delighted to meet him. They even take him in as they hear his adoptive parents have died in car accident and he's looking for a place to stay during his business studies just like Greg, to pay for which he held various jobs, even in Rio. The only one who remains suspicious is Tara, who doesn't want to be the kid sister and starts looking for holes is Jamie's story, going trough his things and having a friend examine his past- there are, since he didn't tell the Norris family about his lover who helps him unconditionally with his sinister hidden agenda.