Priest Plot Line

Karl and Jessamine:

They both are turned into human vampires when a mission with several other Priests goes wrong.
After this they have a few months of fighting as they settle into their new lifestyle

Jessamine goes out into a human town one day in search of a book she had been wanting, however, because she has not fed in a long while, she is very weak, being in the Sun makes this worse.
When she faints, she is found by a human in the town and they find out she is a vampire, she is taken back to the Church and the village agree that she is to be burnt.
Karl arrives in time to save her

From this a hating of humans is born in Karl's heart and it begins to change him, from this point the film plot begins with his kidnapping of Roberts daughter.

After the massacre of the town, including all of the innocent children, the relationship between Karl and Jessamine ends, as she couldnt bare to be with him in a romantic manner, him being so far removed from the man that she loved, she gives him an ultimatium, to either stop his plans and be with her, or to continue and lose her.
He chooses to continue.
Although she stays in the train with him, she does so because she still loves him, and wants to keep him safe.

In the final train fight she saves Karl, and they both are given redemption by Robert, who allows them both to live, as long as Jessamine swears to try and changes Karl's ways.

To make matters worse, when Jessamine and Karl have their falling out over the slaughter of the village, Jessamine is pregnant with his child! This makes the slaughter of the children much more powerful on Jessamine who, while not sure, suspects that she might be pregnant with Karl's child.