A travelling commercial partner's chance decision to follow a slow lorry leads him into a secluded woodland where he uncovers a suspicious cargo and becomes entangled with an amateur conspiracy. The initial improvised schemes give way to a more dangerous professional organization whose secrets involve illicit transport and ultimately murder. A methodical criminal investigation led by an inspector pieces together clues, deciphers double-crosses, and traces lorry movements to expose the syndicate. The narrative alternates between the bungled efforts of amateurs and the systematic work of seasoned detectives until the conspiracy is resolved.