Pretty soon I'll post a short story that demonstrates about what I'm trying to do.
Here's a summary.
In the furthest corner of the Imperium there's an imperial world contested between a continent loyal to the imperium, and one that broke away. A bitter war rages as the loyalists attempt to bring the renegade continent back into the Imperial fold and punish the traitors. Conveniently timed warp storms have so far prevented the Imperial Navy from arriving and bringing reinforcements.
Many Eldar Outcasts have long since found refuge in the continent of the renegades (there's a webway portal there), and occasionally intervene to keep the Imperials from winning. A band of outcasts have holed up in a remote part of the renegade continent, and among them is one of the main characters who will eventually become a Harlequin.
He temporarily leaves (out of boredom and the need to satiate curiosity), and when he returns he sees the cut off remnants of an Imperial Army in the final stages of eradicating his compatriots. Enraged (and bored), he wages a one-man shadow war against the remnants (with his longrifle and his blade), laughing all the way, never worried about death. He manages to kill most of them before being injured by a frag explosion.
He figures he might get one more shot before being taken out when a mysterious figure arrives as a blur (this is the Solitaire, but our protagonist doesn't know this yet). The final twenty guardsmen are decimated by this figure. Still wounded and on the ground, the figure approaches. He takes note of how he looks and walks. The figure has no face, but seems to be morbidly fascinated. As our hero is about to ask who this figure is, the figure runs away in a blur. Our protagonist passes out.
He awakens to find his wounds healed, and the spirit stones of his comrades safely secured. In the room are other Eldar Outcasts and renegade humans. He asks about this mysterious figure, and the Outcasts and the humans give different accounts of what they know or have seen.
Apparently, more Eldar - not just outcasts - have taken an in interest in seeing this faction prevail. Why is this? After more digging, he finds out that a band of Harlequins have also infiltrated this world. He is determined to find out more...
Cegorach's plans are beginning to unfold.