The Dark Stone is a form of Zekrom.
Clay finds the Dark Stone, presumably in Twist Mountain (but unconfirmed). Clay feels uneasy about it and thus asks Lenora to come take it off his hands. Unknown to either, the Shadow Triad intends to steal it from them in order to get Zekrom.
Lenora and Hawes guard the Dark Stone in their museum for some time with tight security before they grows lax and lessen security because it is frightening their guests. The Shadow Triad then steals the Dark Stone.
- ↑ Pokémon Adventures: BW Chapter 14