Looking for a specific Honorverse novel

Way back when, I was buying Honorverse novels as fast as
Weber could write them. (Main series, not the side stories.)

Then, I hit the one where some unknown force did something
to turn one of Honor's trusted armsmen into a meat puppet
in an attempt to assassinate her, while the mind of the
armsman, completely disconnected from control of his body,
frantically tried to stop what his body was doing.

Hit the end of the novel ... whoever did it was still
unknown, not a clue who or what it was.

At that point, given the pace of new books, I wanted to
hold off on reading more until I knew I could read through
to where a defense/detection was found, whoever did this
got revealed, and they got thrown alive into the Lake of
Fire or some reasonable facsimile. Or some resolution of
this issue, anyway.

And, I kind of lost track.

So, which book was this?  I'm planning to go to a con where
Weber is the GoH this fall, and I'd like to get back into
it; read the rest of the books I haven't read yet.

--
Mike Van Pelt       |  "I don't advise it unless you're nuts."
mvp at calweb.com   |   -- Ray Wilkinson, after riding out Hurricane
KE6BVH              |      Ike on Surfside Beach in Galveston