S1·E29 Faltering Friendship

One morning, a train is found thrown off the track, all out energy. While everyone watches him worriedly, the train wakes up, pointing the finger at Duke as the attacker. Everyone starts to suspect Duke again and asks him for an explanation. Kay fights for Duke's innocence, but Alf and Duck also start to get suspicious of Duke. At last, Duke declares that he'll get locked up.