In this experiment, learners separate different types of molecules in marker inks (using a technique called "thin layer chromatography"). Learners mark dots at the bottom of a strip of paper (stationary phase) and put the paper into a cup of water (liquid mobile phase) to see how the inks separate. The experiment is repeated with more colors, then mixtures of colors. The final investigation is to figure out who took a cookie, by analyzing the ink used to write a note left in the cookie jar, and comparing the ink to markers taken from two suspects. The activity is written as part of a kit, but can be done without the kit.