I recently finished The Emperor Protects with my players, and we're taking a break as I prepare our next campaign. During the final mission, I decided (via the chaos-device showing past and futures) to show my Dark Angel player the Fall of Caliban, just to screw him up .
Note that the character has been sent in the DeathWatch because he was not "mentaly able" to know the truth about his chapter, but was still a great warrior. So right now, as you can imagine, his character his pretty much f*cked up in the head. After the campaign, he asked me if we could do sessions to evolve this part of the character. Of course, I agreed, and because I highly value what my players want for their characters instead of evolving them myslef (basically, I asked my player if he wants to do a "side quest" to evolve his character instead of throwing it in his face), I asked him what was his plan for his Dark Angel. But he doesn't really know, telling me that he'll see what the chaplain will tell him. I personnaly took it as a "Do what you want with my character" (note that he already told me that it's not because his not interested in this, but really he can't decide which path to choose).
So finally, here's my question : how would you initate a Dark Angel to its chapter's secrets ? I think i'll have him fights some chaos dudes and reports to the chaplain every time, where his faith would be tested as he truly "understands" the nature of betrayal. Finally, he would have to hunt some Fallen (knowing they are Dark Angels only when he see the chapter icon on their shoulders) and interrogate them as a final test. I also plan to have two side characters, the chaplain and a deathwing veteran, with one of them wanting him to know the truth while the other doesn't (eventually, depending on his actions while fighting traitors, this two characters may evolve to both accept him or reject him).