When Mortarion, daemon primarch of the Death Guard Traitor Legion, awakes in a strange garden with no memory of who he is, he cannot know what delights await him in its rotting tranquility. Above all things, Papa Nurgle is a generous god.
There are certain elements I draw from this. First of all, The Primarchs-spinn-off series will have short stories in them. Why I do not get as the regular series already have those. This time they focus on the Primarchs I guess. Second of, this seems to be set way after the Heresy when Mortarion is a Daemon Primarch. Will it have flashbacks? Perhaps. But it seems to be too short for such a thing. Could this be a set-up for the actual Primarchs-novella about Mortarion? Perhaps. Maybe Guy Haley will penn that story too.