Deception evolved as a fundamental aspect of human social interaction. Although numerous studies have examined behavioural cues to deception, most have involved inconsequential lies and unmotivated liars in a laboratory context. With a novel paradigm, the present dissertation is the most comprehensive study to date of the behavioural consequences of extremely high-stakes, real-life deception relative to comparable real-life sincere displays using three communication channels: speech, body language, and emotional facial expressions. Televised footage of a large international sample of individuals (N = 78) emotionally pleading to the public for the return of a missing relative was meticulously coded frame by frame (30 frames per second, for a total of 98,393 coded frames). About half of the pleaders eventually were convicted of killing the missing person based on overwhelming evidence. Failed attempts to simulate sadness and leakage of happiness revealed deceptive pleaders’ covert emotions, as hypothesized based on observations by Charles Darwin and a contemporary understanding of human facial innervation. Specifically, full contraction of the frontalis (failed attempts to appear sad) muscles and subtle contraction of the zygomatic major (masking smiles) were more commonly identified in the faces of deceptive pleaders. In contrast, prototypical aspects of “grief,” as produced by the corrugator supercilli, and depressor anguli oris muscles were more often contracted in the faces of genuine than deceptive pleaders. In addition, liars used fewer words, but more tentative words than truth-tellers, likely relating to increased cognitive load and psychological distancing. Further, simultaneous attention to each of these cues – tapping emotional arousal, cognitive load, and psychological distancing theories of deceptive behaviour – discriminated 90% of pleaders correctly, supporting the multiple cue approach to deception detection. Findings further reveal the secrets of the human face and contribute to our understanding of human communication more generally.