One day, fourteen-year-old Ivan meets a remarkable girl, who persuades him to jump into an ice-cold river in the middle of winter. Believing that this is his chance to pull off a great coup – didn't he overhear the two teenagers whispering about treasure? – a nasty, little crook jumps in after them, his brother in tow. The policeman Peter Bunny – whose surname is a general source of mirth – sees an opportunity to prove his bravery, once and for all, and he too plunges into the icy water. Instead of contracting hypothermia, these crazy five discover The City with the Blue Door, a giant horse answering to the name of Terminator, who can change colour from black to white in a hoofbeat, the terrible dragon Smej Gorynitsch and – last but not least – the silver-grey wolf, without whose help all would be lost.