Erfworld 76, page 70

[Yogi]

1. Team Stanley already knows that Ansom loves Jillian, which is what matters here. They also know she just pulled his boops out of the fire, or is valiantly trying to, at any rate. It doesn't take much pie brains to figure out that she'll be very valuable as a hostage, and that croaking her will up the ante with Ansom.

Actually, Ansom is suspecting that she's a traitor, and he's not the only one. He's already suspicious of all the times she was captured. Hence, if Jillian is captured AGAIN, he might not be willing to go after her, especially considering what happened the last time he tried.

2. Ansom will inevitably find out sooner or later, which also should be obvious.

How?