[@Jbcool] 

So basically, during 999.M41 - The 13th Black Crusade, The Thousand Sons are doing a few things. There's the battle on Fenris, where Magnus manifests and ultimately brings Sortiarius into the materium near Prospero, but there's also a contingent of Thousand Sons that are scouring territory near Prospero. They are invading Imperial worlds to claim them. The Thousand Sons do have a large portion of mortal units, the mindless Rubrics, and also the powerful sorcerers, who are bascialy librarian chaos marines. 

I'm sure I could play one of the sorcerers, aka: a lesser Sorcerer-champion of Tzeentch, a thrall, or an aspiring sorcerer. Say his thrallband got routed and he fled either by teleportation or warp rift or starship and meets up with the other players. Now do you know what I mean?