In the late nineteenth century, Nick Knight was an archaeologist working on a dig at the Mayan site of Altun Kinal. There he found a jade cup, one of a pair that were used in a ritual that, among other things, involved pouring blood from one to the other. This ritual was supposed to provide a cure for vampirism. Before he could come upon the other cup, though, the excavation had to be abandoned because of mysterious attacks on the workers—presumably by LaCroix, who would certainly not want Nick to find a cure.
In 1988, Nick moved to Toronto. Three years later, the Royal Ontario Museum showed an exhibit of recently excavated Mayan artifacts. Among them was a second jade cup. The news report of the exhibit brought LaCroix to Toronto post haste—but secretly, lest Nick realize his intentions. He broke into the museum, killed the security guard on duty, and stole the cup. Nick was one of the detectives assigned to investigate the murder of the guard; and, when he realized what sort of artifact had been stolen, he immediately suspected that LaCroix was in town.
His first confrontation with LaCroix resulted in the stolen cup being broken, thereby making it impossible for him to complete the ritual. At the end of "Dark Knight: The Second Chapter", therefore, when Nick ostensibly returned the stolen cup to the museum, he actually substituted the jade cup he had dug up a century earlier.