From the introduction:
The king's sorcerer has gone rogue and seeks to uncover a massive ancient construct with devastating power. The party is sent to stop him, but in the end the group must choose whether they should destroy the construction or hand it over to the king.
...
The king or another powerful noble contacts the party wanting their help on a delicate and discrete problem, and emphasizes the need for their discretion. His court sorceror has gone rogue, taking an important magic item that is used to activate large constructs. The sorceror was last seen heading into an old tomb known for housing ancient constructs. The noble asks that the party stops the sorceror and recovers any construct he activates with the item, since the stone is his property and once used to claim a construct it can't be re-used.