The Flight of the Eisenstein picks up just after the Isstvan III traitor forces attack and massacre of loyal Space Marines, continuing the adventures of Death Guard captain Nathaniel Garro, who witnessed the rebellion, stole a ship and is trying to escape the Isstvan system to warn the emperor about Horus and some primarchs betrayal.
Without spoiling much, we'll read not only about battles between loyal and traitors, between space marine and demons, but also interal fights inside the survivor minds trying to digest the fact that most of what they stood for has been corrupted, that they will face their own brothers (and worse) in battle.
Continuing exactly where the third book left, was an enjoyable and nice paced read, with some tense moments and sometimes grotesque descriptions of some chaos taints.