Smile on the pavement

The routine of St. Petersburg tour guide Artem Zubarev intersects twice within a couple of days with murders: first, a dead girl is found in the Alexandrovsky Garden, who had approached him for help the day before, and then, right before his eyes, a woman is thrown off a river tram. Coincidence? Bad luck? Either way, Artem unwillingly becomes embroiled in a series of strange events, and the retired investigator Bragin has a precise and succinct definition for this series: a series. In reality, there are many more murders, and the connecting link between them is a smiley face drawn near the crime scene.
However, a similar series of mysterious deaths occurred in St. Petersburg just before the revolution — at least that’s what is stated in the diary of a Russian emigrant that Artem randomly comes across. Perhaps this diary will be the key to solving the current murders and deciphering the meaning of the smileys drawn on the pavement?