True zombieism cure requires: the Agabayani research from Wentachee, the European datadump from Penticton, and The Vial of Monkey Blood

For the Vial of Monkey Blood you will need to Begin in a New City that is NOT Abbotsford, Vancouver or Snoqualmie.

Isolate, but DO NOT capture one Mall WITH loot and one Motel WITH loot. Just capture all surrounding tiles and place stakes on the mall and motel. We will use these later. If your city does not have these, or the opposing factions capture them before your ready the quest cannot be completed here. Wait for next city.

The following four events (and the Signposts Research) can be completed in any order, but the last two must be completed within a span of 40 days. We thus recommend doing them in the following order.
Gretchen will trigger once two events complete and signposts are researched.

Trashy Romance Novel
Requires (five Schools) and City Hall to meet with a faction, until interlocutor offers to help you stock them with books. Choose the Fiction books.

Newspaper
Send a group of survivors on a mission to a tile that is next to a zombie mob (and that, in your judgment, is in the path of the zombie mob; this won’t work if the zombie mob goes in a different direction). The group of survivors must include at least one active Engineer
Continue to read the paper

Sell Cricket Bat to Gustav
Sell the (Cricket Bat) to Gustav. Gustav will talk about "ze game of ze gentle men". (Save your game; if the event text does not happen, load your game from the earlier point, and try to adjust (such as just selling the Cricket Bat and not buying anything).
This event should be done third because Gustav does show up on a regular basis, but isn't around all the time.

Mall Pet Store
Scavenge the unclaimed mall with loot using a survivor that has at least Level 10 in Scavenging, which may be reached with weapons and items such as a Fire Axe and Backpack.
The event text will say that the scavenger finished the mission early and has time to do something else. Choose to go to the Pet Store.

If at least two of the above first-stage events, the Signposts research has been completed and there is room in your fortress for another survivor, a female engineer named "Gretchen" with blond hair and a white dustmask over her mouth will join your fortress.. For clarity, this is Isa Gretchen van Nooten; you will not interact with any other "van Nooten".

Injure a Survivor
You will need an injured survivor in your fortress. If you don't have any injured survivors, then send out a survivor you're willing sacrifice on a dangerous mission to get him or her injured; try to keep the Danger level of the mission in the red. While the survivor is recovering, there will be an event where Gretchen, specifically, wakes you to inform you that the injured survivor has come down with zombieism; this will kill the survivor.
It is possible that the injured survivor will recover without Gretchen waking you up to tell you that the survivor has zombieism. In this case, you will need to injure the survivor again, or injure someone else.

Gretchen's Departure (Fail Condition)
After some time, Gretchen will get into a fight with a random survivor in your fortress. (The text says that Gretchen and the survivor were cleaning a storeroom, the survivor killed a rat, and Gretchen went berserk.) If you have a Level 7 Leader, you can try talking to Gretchen, otherwise you can only ask her to leave. No matter which you choose, Gretchen will leave the fortress (and the statistics will register her as a killed survivor). If she leaves before you complete ALL four first stage events you fail.

This event will occur some time after Gretchen's arrival, regardless of whether or not all of the other above events have occurred. This is why you are under a time limit the moment Gretchen arrives in the fortress.

WAIT UNTIL GRETCHEN LEAVES

Scavenge the motel (with loot) that you set aside and that has not been captured.
You will be directed to a mission in a random Hospital outside your fortress. The game will add one if needed. The event options for the hospital just have you searching through the rooms that had an I.G.v.N.

Once the Hospital mission is complete, you will then be directed to a mission in a random School outside your fortress. The game will add one if needed. Regardless of what dialog options you choose, you will obtain the vial of Monkey Blood.