This is a typical story from the 'cold war' era. A group of kids play on a quiet street in Sofia. From a nearby window falls a key. The helpful youngsters quickly return it to the owner, but in the haste switch the keys. The unintentional error disentangles a whole spy story. The young detectives doubt the good intentions of the man they tried to help. It turns out that the key is from a secret apartment where saboteurs are hiding. The secret network is exposed to the authorities and the kids feel like heroes.
| Writing | Pavel Vezhinov | Writer |
| Directing | Petar B. Vasilev | Director |
| Sound | Kiril Popov | Sound |
| Sound | Parashkev Hadzhiev | Music |
| Camera | Boncho Karastoyanov | Director of Photography |
| Art | Tzenko Boyadzhiev | Production Design |
| Costume & Make-Up | Maria Sotirova | Costume Design |
| Editing | Katya Vasileva | Editor |
| Production | Doncho Todorov | Producer |
