I've been reading through the book "Fulgrim".
In the 19th chapter Fulgrim tries to convince Ferrus to join the traitor forces. One of the things he says in the argument is:
Lorgar and Angron are ready to strike and Mortarian will soon be with us.
Later on in chapter 21 when Ferrus hears from Dorn he is told that several Primarchs have been reached and are assembling to destroy the traitors.
Salamanders, Alpha Legion, Iron Warriors, Word Bearers, Raven Guard and Night Lords. Including the Iron Hands that's seven entire legions. Horus doesn't stand a chance.
This seems like a huge plot hole. Why wouldn't he be suspicious of the Word Bearers and at least mention to the other legions that he was already told they are traitors?