One of the current challenges in forensics is establishment of a connection between an individual and substances to which they have been exposed, and which might have relevance in crime scene investigation. An example of a situation in which this arises is when an individual has handled, and is under the influence of any one of a large number of currently unscheduled plant-based mind-altering substances. In such instances as a medical emergency or a crime scene investigation, one way to establish a connection between an individual and their exposure to such substances is to take advantage of the high information content of their fingerprint. The fingerprint pattern not only establishes the identity of the individual, but also contains rarely exploited chemical information about molecules to which they have been exposed that might have a bearing on a crime. If the fingerprint image is based on the spatial distribution of diagnostic molecular markers indicative of a substance, then an individual’s identity can be definitively tied to exposure to the substance. The fingerprint image derived from the spatial distribution of diagnostic molecules can be obtained by mass spectrometry imaging (MSI). Here, we demonstrate how the handling by an individual of a plant-derived psychoactive brew called ayahuasca can be established through determination, by matrix-assisted laser desorption ionization (MALDI) MSI, of ion images featuring biomarkers from the plants from which the brew is made.