The spies somehow knew what they'd just seen weren't uniforms.

Senjin had very little time - something the spy knew - and so was at a disadvantage.

"Or that the spy would know enough to steal one."

They would remain in wolf form until the siege, so that no spy would know.

How could he or his spies know anything of that?

"After all, your spies already know of my contacts with Thebes."

There is one thing which his spy does not know.

Even if he did, a spy could not know the key-words, without reading the letter.

Also, the spy should know how to get out of this cell, in case she needed to make a secret report.

But that's what they want you to believe: we spies know more about everything than you do, and sooner.