Willful Ignorance(Occult Origins pg. 12): The subject gains the ability to tell one undetectable lie. When the subject attempts to lie, the mesmerist can trigger this trick. That particular lie resists truth-detecting magic, and creatures attempting to use such magic must succeed at a caster level check against a DC equal to 15 + the mesmerist’s class level to succeed; failure means the magic doesn’t detect the subject’s lie or force her to speak only the truth.
This is a masterful trick.