The new guy’s name is James Aubrey, as reported by TVLine. He is described as a junior agent in his 20s who is a “charming, charismatic, politically ambitious” sort of guy.
It sounds like Aubrey is going to be a younger version of Booth, with a lot more drive for the political arena. Booth, meanwhile, isn’t likely to have much interest in politics after the government turned on him at the end of the most recent season.
The role has not yet been cast and there is no information on how much Aubrey might appear in Season 10. Fans will have to wait until the show returns to FOX in the fall to find out.