Jonathan sets out to acquire ingredients required to create an antidote that will help in the fight against the epidemic. To defeat The Disaster, you need to acquire three ingredients that are scattered across London.
At this point, you are able to create a very strong, legendary one-handed weapon. True Dragonbane - to get it, you need to complete the "Pandora's Box" investigation for Usher Talltree. Details can be found on a separate page of our guide.
When you're ready, go talk to Lady Ashbury at her property. Tell her it was her blood that contributed to Harriet Jones' infection. The woman will run away, and you will be forced to get the three ingredients of the antidote.
The first ingredient will be the blood of William Marshall. To get it, you have to get to the Ascalon club and talk to Lord Redgrav.
If you have turned Aloysius Dawson into a vampire, you can enter through the main door and talk to Lord directly; after the dialogue, you'll get the first component of the antidote.
If you were expelled from the Ascalon club, you must enter the through the side entrance and defeat a strong Ekon. After the fight, you can talk to Redgrav and demand Marshall's blood.
The next step is to get some insulin. To find it, you have to go back to Pembroke Hospital and enter the Old Morgue.
Once there, run up the stairs. A skirmish with several Priwen Guards awaits you, at levels around 35. Take care of the enemies take the insulin from the table.
The last component of the antidote is located at the cemetery. You'll meet McCullum there, a man who has a few drops of King Arthur's blood.
Depending on your decision, McCullum will be a human or a vampire. This, however, is irrelevant for the dialogue - the man will give you blood in either case.
When you have acquired all three ingredients, go to the safehouse and create the antidote. Now you are ready to face a Disaster.