21. The enemy's spies who have come to spy on us must be sought out, tempted with bribes, led away and comfortably housed. Thus they will become converted spies and available for our service.
22. It is through the information brought by the converted spy that we are able to acquire and employ local and inward spies.
23. It is owing to his information, again, that we can cause the doomed spy to carry false tidings to the enemy.
24. Lastly, it is by his information that the surviving spy can be used on appointed occasions.