During their short ride to the plane, Talia and Damon spoke through their private mind-link, careful so that no one overhears them.
Talia told Damon that she injected Dex with the same potion that Marcy got, and she also admitted that Alpha Magnus got a dose of the same after her soft approach failed.
Damon couldn't believe this. Marcy was one thing, but Dex was a Guardian and Alpha Magnus was a powerful Alpha. If she made one mistake, things could end badly. But he knew Talia did it to save herself, and he didn't have time to complain because Talia told him that Guardians were witches and that she suspected there was more to the Sphere of Power than what Dex told them.
Damon agreed that the business with that spherical object was fishy. If it was just into looking at someone's potential or an unknown future, they wouldn't insist on Talia re-doing the test.