There are many contexts in which investigators want to interview suspects about their intentions without alerting the suspects that they are actually being interviewed. In the present experiment, we developed and tested an “undercover interviewing” technique. Liars were instructed to run a crime-related reconnaissance mission to a nearby island and were further instructed to generate an innocent cover-up story to hide their criminal intentions. On arrival at the hovercraft terminal, an undercover agent, acting in the role of either a doctoral student or an amateur photographer, approached the liars and asked apparently innocuous questions about their forthcoming trip. Actual tourists using the hovercraft terminal served as a control group. The questions were designed in the knowledge that liars tend to avoid and escape and do not expect spatial questions and that truth tellers have detailed representations of intentions they are about to execute. In support of the hypotheses, liars were less willing to be photographed, less accurate in identifying the places they planned to visit, and less concrete and more uncertain when describing their intentions.