I was re-reading Black Library' Fulgrim by McNeill recently. I found a little inconsistency, well major plot flaw to be honest, therein on my re-reading.
In the encounter between Ferrus Manus and Fulgrim, the primarch of the Emperor's Children tells Ferrus that "Lorgar and Angron are ready to strike, and Mortarion will soon be with us."
Later on, on the sands of Istvaan V no less, Ferrus Manus is well-pleased to see his brothers, Lorgar included make landfall to apparently help the loyalist cause.
So, what could be the cause of this?
Clearly it could just be an overlooked facet.
Or, alternatively, perhaps Ferrus just thought Fulgrim was flat-out lying. Indeed, later on, Dorn's orders simply state that the traitors are Horus, Fulgrim, Mortarion and Angron. Nothing about Lorgar. Hence he has no reason to yet doubt that Lorgar has turned traitor.
Anyway, I just caught this today, so thought I'd jot it down here!