Where we left off:
Lord Haaf-Mersey has rounded up a couple of renegades for Isran, and these renegades have been sent to Castle Dawnguard. After spending some time at Lakeview Manor LHM has returned to Dawnguard, where he now finds somebody waiting for him. 
"Serana?" But such cannot be!"
"You probably weren't expecting to see me again."
The pair stands in an antechamber, away from the main portion of the castle. Isran is also present, as well as Mjoll the Lioness, Haaf-Mersey's new warrior companion.
"But ye are here?" the Lord says. "Of what austerity have ye the confidence to make court amongst such valiant, mortal men as these?" Haaf-Mersey looks towards the stone floor they stand on. It is sticky with blood.
"I'd rather not be here either", Serana says plainly. "But I needed to talk to you. It's important. So please just listen. It's....it's about me, and the Elder Scroll that was buried with me."
As her words calmly issue from her lips, Haaf-Mersey's heart initially
races, his senses on high alert, but then it suddenly slows. A sort of calmness takes over. It's those
eyes of hers.
"Scroll?....Ye maketh mention of a scroll?" ..
.Everything is okay, he thinks.
It's just her. It's just Serana."The reason I had it and why I was down there... it all comes back to my father. He's not such a good person, as you may have already figured out."
Did she feed? the Lord thinks. He is still calm, but also alarmed.
Did she take another life right here? With all of them standing around watching? ...Haaf-Mersey's thoughts are
immediately answered by Serana's mind, even as she speaks to him and Isran with her physical mouth. ....
Do not be alarmed. I do what I have to do to survive, just like you. He was a captured bandit, the sort of man you kill everyday. I rid him of his miserable mortal life, just as you have many times....it is as if the Lord stands in two rooms at once. In one room, all four of them (he, Serana, Isran, and Mjoll) are standing present. In the
other room, it is only Haaf-Mersey and Serana.
There now....it's okay.... she tells him in this other room, causing him to put down his guard completely. He cannot even reply back, he's so calmed.
"............... good fight!" What do you make of that?" Mjoll babbles behind the group, in her own little world.
Lord Haaf-Mersey realizes that he's fully back in this room with Mjoll, Isran, and Serana; the
other room where he and the vampire spoke alone is now gone. "Thine father?" Haaf-Mersey replies dumbly, now confused. "... an Elder Scroll? ... How does such ....?" his thoughts are so scrambled...
"It's pointless and vain, like all prophecies" Serana tries to explain. "It is said that vampires would no longer fear the sun. That's what my father was after, he wants to control the sun." ...Serana explains that to keep the scroll from her father, she had been entombed, hidden deeply within Dimhollow Crypt. And now, she's made it to Dawnguard, where she feels safe and needs his help.
"I am of felicity that ye have made thy presence of...." the Lord says, dumbly. He doesn't know what to say. He's that dumbfounded lad back in school, all over again. "...presence of mind".
"I did. But something about you makes me think I can trust you."
The Lord is shocked once again. Serana seems to want to
assist Dawnguard. She comes to the castle, somehow makes it inside without being killed, and is still
here. She
waited for him. Could this be a ploy?
"Well, what is next, then? ..Ye would prefer to make employ of this stronghold of vampire hunters? Such is of clarity?"
"That was the plan, yes. Assuming the rest of them can trust a vampire. Come on...I'll need you to help convince them."
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12:15 pm"Alright" Isran says as the Lord turns to Dawnguard's leader. "You've heard what she has to say. Now tell me, is there any reason why I shouldn't kill this blood-sucking fiend right now?"
Lord Haaf-Mersey feels slighted by Isran's words. It's as if Isran is insulting his sister.
"Mind you!" the crusader scoffs in lower Tamriellic tongue. "Serana has made preparations, and performed visitation of her own sort of accord, Isran. ...And presented us her tale. We can deliver her away from eternal life, perhaps, but perhaps Serana might also make provision towards vital assistance, in our fight against the derisive evil which now inhabits Skyrim. Perhaps Serana might
also knoweth of the trappings of her father's home. A sort of spy, a sort of accolade, might she be. And in full assistance. What sayeth ye upon such?"
"Set my hatred aside? Not a chance! It's what keeps me strong." Isran answers.
"I have seen the light, Isran. The light that shineth of Julianos, Lord of logics, reasonings. Serana is not of pertubation. And ye shalt make one mighty decision of wrongful misdoinings, should ye not gather with open arms and mind Serana's provisional offer."
Lord Haaf-Mersey realizes he is saying these words
himself, without any of Serana's charms or urgings. It's as if she is allowing him to make up his own mind about this situation. She is honestly leaving her fate up to him.
"You'd better know what you're doing," Isran says coldly.
It can stay for now, but if it so much as lays a finger on anyone here, you'll be responsible." Isran now turns to the vampire "....You hear me? You so much as lay a finger on anyone here and you're dead. But I realize your resource is an asset to Castle Dawnguard. In the meantime, don't make me regret my sudden outburst of generosity. Because if you do, your friend is going to pay for it."
"Thank you for you kindness," Serana replies with sarcasm. "I'll remember it the next time I'm feeling hungry."
The lord finds himself suppressing a giggle at this. He's fully under the vampir's charm, once again, and does not realize it.
"Are you ready?" Serana asks the Lord now as Mjoll babbles again from behind like an eager schoolgirl. Serana then explains that nobody can read the scroll, except for a group called the Moth Priests, who only reside in Cyrodiil.
"I heard a new scholar arrived from Cyrodiil not long ago..." Isran replies, but refuses to help the vampire figure out where the Priest might be staying. He
does suggest trying various inns, though.
"What sayeth ye?" the Lord asks Serana. "I am of desire to make findings of this scholar. Have ye any preconceptions of locating?"
"Well back before I..I... you know...the College of Winterhold was the first place I'd go for many magics or historical things. I ....I realize I can come with you, but I don't know if I can trust your friend. Let me know if you want me to come along."
Lord Haaf-Mersey turns to his companion, Mjoll the Lioness.
I must choose her? Or choose her? The Lord expects his thoughts will be answered again by Serana, as she speaks to him in that other room. But this does not happen. Matter of fact, Serana calmly leaves the antechamber. No charming, and no 'urging.'
"I need to have solitude with mine thoughts...", Lord Haaf-Mersey says diplomatically. "..that mine choices ring true, and follow mine heart".
Serana, surprisingly, allows this to happen.