Mind Thief by Chris Philpott

The spectator imagines he has to get this valuable object home and hide it - but someone is trying to steal it from him! The performer shows him pictures and words in a spiral-bound book with options to get home and hide the object: on wide thoroughfares or narrow alleys, entering his home from the front door or back, hiding it in the bedroom of basement. The spectator never tells the performer his choices. 

The performer then explains this has all been a con job: the real valuable object is the thought in the spectator's mind, the thief is the magician, trying to steal that thought; and the imagination game told the magician everything he needs to know about how the spectator thinks: for example, his choice of whether to go home on a wide street versus a narrow alley reveals how comfortable they would be sneaking this object home through a crowd and helps the performer interpret their body language. The performer then tells the spectator not only what the valuable object is, but where in his house he's hidden it.