If you don’t mind spoilers, I can fill you in:

Basically the homunculi failed. An inquisitor and a custodian put him down.

The Dark Eldar agreed to fix the throne and seemed to intend to do it, but they also wanted a drop of the Emperor’s blood (or something like that) to do something horrific with.

Mars, High Lords and as you said factions of the Inquisition made the deal.

After the hominculi was killed A couple inquisitors and some Custodes, found out there was webway portal on Luna with the Mechanicus guarding it. They fought through the Mechanicus, entered the webway and tracked down the Dark Eldar who were meeting with the fabricator general. Shit went down, pretty much everyone died. That entire plot more or less wrapped itself up.

The big plot development is the Mechanicus and the Dark Eldar both believe the Golden Throne is going to fail in less than 100 years.