The Unholy Grail was the object Alexis Crowshaw was hired to steal from one of the Vatican's storage warehouses. She hadn't been told exactly what the object was, just that it was dangerous and that she would be aid well for her effort. It came in a sealed metal box that Alexis, far too curious, decided to open.
Upon discovering what it actually was, she took the box to the people who'd hired her for the meetup. They attempted to kill her, and she fled with the grail in hand to Saskatoon, SK. Thinking that they would not find her- or at least were less likely to- she hid the grail in a storage locker in Clavet, SK.
With the Squad
The grail was again taken by the same people who had originally hired her to steal the grail, partway through her time with the original squad. It led to her confession to the Squad that it was her fault it was in Saskatchewan. The hunt for it and some missing children led them to a church under construction in ------,SK. The group had kidnapped the children and was using them in an infernal ritual to gain the power that the Unholy Grail had.
The Squad managed to save the children, and while most of the Squad was distracted trying to help revive the passed out children, Alexis stole the grail out from under their noses. They knew she had swiped it, but could not find it on her. She kept the grail under tight security for her remaining time with the Squad. She left a while after that and took it with her while she went to train under Eric Becker.
After Evander's departure from the Spook Squad, Alexis returned with the grail. She traded the knowledge of the grail's whereabouts to Evander Summers for info on their enemies location.
Alexis, after some planning between her and Eric Becker, took it to the final battle between the Saskatoon Spook Squad and their enemies, the Concerned Citizens. It was to be a last resort, if things were going very badly.
Alexis had been tasked to defend Ed by Kaki, and in near the end, used it to save him and bring Marion, Ed's enemy and the new hand of Poseidon to them. Hellfire reigned down from the sky and eliminated the remaining enemy troops in the abandoned church and chains of hellfire surrounded Marion and dragged him, kneeling to Ed's feet.
After the battle, Kaki let Alexis go. Alexis used the grail and saved Ed, so the Warden let ignored what she had seen and vowed to watch Alexis from then on to make sure she wasn't breaking any more laws.
Alexis returned to her work at the Venatori and to her work with Eric. She still uses it from time to time, in battle and in other torments.