The designer of space drilling rigs for interplanetary vehicles, Professor Milovidov, admits to television journalist Babochkin that in 1970, the return vehicle of the Luna-16 station delivered to Earth not 101 grams of lunar soil taken in the Sea of Plenty region, as is officially believed, but 136. Two fragments of lunar ilmenite were stolen when the capsule with soil was opened by production shop engineer Kern. One of these “pebbles,” contrary to the professor’s wishes, ended up in his possession. Milovidov believes that his life is nearing its end and he decides to give “his” fragment to the journalist. However, moonstone has some strange properties, especially during the full moon, and, according to the designer, it should not be trusted... All events and characters in the story are fictitious and have nothing in common with real scientists and designers who took part in the Soviet project "Luna-16" .