An ancient passenger steamer with a strange name for the Yenisei “Thames” set off on its next voyage. Things went swimmingly. The crew, led by the stern Siberian captain Ilya Samarin, coped with their duties. Passengers, including millionaire German Rostotsky, enjoyed the views. And it had to happen that Galina Ivanovna, who accompanied a group of schoolchildren, persuaded the captain to change the route. Just a little bit, just to show the children some mysterious place. The captain gave the command. The Thames headed towards the shore, and... No one understood what happened. Just now the steamboat was splashing along the harsh waters of the Yenisei, and the taiga stretched beyond the side, and now it is already cutting through the muddy waters of an unknown river. And along the banks there is a real tropical jungle. Neither captain Samarin nor businessman Rostotsky suspected that these thickets had nothing in common with the tropics of the earth...