Murder in a locked room, about which it is said: “... Karl himself would have liked this, given his passion for detective stories. If he were to die, he would prefer it to happen in a locked room. And not just in a locked room, but in a room protected by the impenetrable Poulard castle, steel walls and windows that cannot be opened.” But he could hardly have liked the solution to this “impossible crime” - the trick used by the authors had already been invented a hundred years ago. years before them and since then has appeared many times in various detective stories...