A substantial number of sexual abuse allegations proves to be false when the investigation is concluded. Close to 35% of the allegations carried in a family or almost family context (that is to say the step-families) are judged ungrounded. This article is dedicated to the allegations of a fifteen year teenager that will prove to be false as for the gestures assigned to the father, but nevertheless revealing of some family truths. From this disturbing clinical situation, we will propose some reflections about the truth to the sense of sincerity, the truth to the sense of probability, reality testing, intergenerational transmissions and acting-out as critical moment for the activity of representation, not only of the teenager but also of her parents*.*.