The prior has set his spies upon it.

He fears lest Brother Emmanuel shall escape; or else the watch is set so that any going forth of his may be known, and he will be set upon and swiftly bound, and carried away to the priory, whence, I fear me, no man will ever see him re-issue." Both the boys had stopped short, and now they looked into each other's faces with dismay.
Their light footfalls had not been heard, nor even the sound of their voices; for a strong breeze had sprung up, and was rustling the leaves overhead, and several birds were singing lustily.

The brothers had time to take in the situation without being seen themselves, and they then drew hack into a leafy covert and spoke in whispers.
"Edred, do thou go back to the house instantly and openly, and warn Brother Emmanuel that he go not forth.

Belike he might come out in search of us, since the hour is long past when we should have been with him.

That must not be.