Well we know he was after Luke's money, but what would he have done to make sure he got it? Just getting Luke to Malta was not going to insure he got the money. He might have done a ransom thing, and it would not have appeared as kidnapping per say, as Luke was going to go with him voluntarily.
It is going to be interesting to find out how Sergio plays into this because he must have some kind of hold on Damien.
I can hardly wait until Martha Byrne returns from maternity leave so Lily will come out of her coma and give old Damien what for :)