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Next morning, the doctor is starting another batch of medicine,  the Queen of Swords has a bounty on her head for stealing the medicine, and Marta is in need of the medicine, her fever rising.  Marta's cards say that the thief is already dead, but Tessa believes Montoya is at the bottom of the missing medicine.
Now whose calling card might this be? Actually, it represents poor Enriquez, who made it home with the medicine, only to be killed by Grisham, who takes the rest and tells his wife to say the man died of fever. Wakie, wakie, Colonel Montoya.

Have you no respect for the dead, Senorita?

No more games, Colonel. What have you done with the medicine?

Do I look like I have any medicine....duh.

Montoya fires at her, but misses. He calls out the guards and the Queen fights her way free. She returns for Enriquez' funeral. His wife reports he has died of the fever. She is now well, however. Grisham seems to know too much. Nothing makes sense to Tessa....duh. She stops by Helm's office.
"There is a sound that is made when a knuckle encounters wood. It's customarily used before entering. I don't know if you've ever heard of it. It's called knocking."

Really, Doctor, I must try it sometime.

You will have to excuse me, Senorita, I'm very busy. (and I have a knot on the back of my head the size of Lubbock.)

How is the medicine coming?

Very slowly with all these interruptions.

Doctor, my servant has fallen ill. Will the medicine be done in time?

In a few days, yes, Senorita.

But can't you die from the fever over a single night? 

Hardly. It would take at least five days if you were otherwise healthy.

If you die overnight, then it's probably because you wasted the time of a very busy doctor.

Tessa sneaks into Grisham's room and starts tossing it, looking for the medicine. Grisham catches her there and she pretends she's come to pay him back for letting Enriquez go.  She's doing the dodge and weave when suddenly.....
Kabooom...Helm's office blows up. What was that? Tessa asks.
Bad timing, Grisham grumbles.
Robert makes it out of the office, then dives back in, but he can't get past the intense heat and flames.
He calls for help and starts the bucket brigade. Barely catching Tessa as she likewise tries to get in the office to save the medicine for Marta.

You should be more careful with your chemicals, Doctor, says Grisham.

There was nothing in there that would explode, Helm answers.

Then, I guess it was an unhappy accident. Grisham grins.

Fever...page four