欲擒故纵 [- qín ɡù zònɡ]leave sb. at large the better to apprehend him; allow sb. more latitude first to keep a tighter rein on him afterwards; let the enemy off in order to catch him later; play cat and mouse (with sb.):
•¶ 我们对他来个欲擒故纵， 看看他还要干些什么。 Let's give him line enough and find out what he is doing.