Aura of Interrogation

You point to up to 4 creatures your choice that you can see or hear. The creatures must make a Charisma saving throw equal to the caster's spellcasting ability. You know whether each creature succeeds or fails on its saving throw.

On a failed save, the spellcaster is able to detect whether creature is speaking a deliberate lie or if it is voluntarily concealing information. 

An affected creature is not aware of the spell unless they are already familiar with its effects. An affected creature can be evasive in its answers or simply refuse to respond, so long as it remains within the boundaries of the truth.