pukunui
Legend
Devlin worked for Luca, didn't he? Why would he tell his accomplice to give Luca the bag, knowing it actually contained a candy rather than the diamond? If she had done so, Luca would have known that Devlin had double-crossed him and gone after him.See. I missed that. I assumed Devlin was double crossing the woman and leaving her with nothing. This DD chases him down, gets the diamond and gives it back.
The simplest answer is that Devlin didn't know the bag had a candy in it when he gave it to the woman to take to Luca.