When doctors Rieux, Castel, and Richard get together to talk about this mysterious, unnamed but plague-like illness, Castel argues that the authorities will tell them the plague has vanished. He’s not too keen on calling it plague.
On the way to a meeting with the Prefect, Castel is nervous that they have no anti-plague serum.
At the meeting, Castel is quick to establish that they’re not yet sure whether this is the plague. Wishful thinking indeed.
Shortly before the town gates are closed, Castel again expresses concern that the serum hasn’t yet arrived from Paris.
Once the gates are shut, Castel and his wife, who was out of town at the time of quarantine, miss each other terribly. This is in spite of the fact that they weren’t too crazy about each other before, but whatever, they’re old and had grown accustomed to each other. So she decides to come back to Oran.
When the serum from Paris doesn’t work, Castel works on devising a new one himself – preferably one that works.
Rieux notes that the plague and their work as doctors has clearly taken its toll on old Dr. Castel.
Castel tries out his anti-plague serum at the end of October on M. Othon’s son Jacques. It doesn’t work, and Jacques dies.
However, by All Souls Day (the start of November), the serum does seem to have some positive effect on others.
The decline of the plague is at least in some part due to Castel’s serum.