I have been dipping into the latest Horus Heresy books and picking the ones that seem most interesting after being disappointed by several of the ones around the middle (Damnation of Pythos in particular).
Throughout the books I have read I have seen the Emperors Children give themselves to Slannesh, Angron become a chaos lord for Khorne and the start of Magnus becoming the emissary for Tzeench.
I have now read a couple of short stories and seen the Death Guard proclaim themselves for Nurgle, however I have not read anything anywhere that shows when and how this actually happened. According to the Death Guard lore there should have been an event involving the Death Guard getting lost in the warp and a deal made with Nurgle by Mortarion to get them out. Have I missed this in one of the books or have the writers of the stories I have read just lost there place in the continuity. If there is a Horus Heresy book where this happens I will add it to my to read list.