Stop, Thief! is a magazine story.
One day, Edward hears the Fat Controller tell the stationmaster that he has left his watch and Lady Hatt's necklace in his office.
Later, Edward sees a man walk into the office and take the jewellery. The man quickly jumps aboard Emily's train just before it departs. Edward demands the thief to stop, but it is too late. Emily steams out of the station with Edward chasing after her and the jewel thief. Edward struggles to keep up until Emily has to stop at a signal which has failed. Edward pulls up close behind Emily and his crew climb down from the cab. Armed with a description of the thief, Edward's driver goes to find the man.
Emily's guard helps the driver search the carriages until they find the man sitting in the very last one. The guard demands that the man hand over the jewellery immediately. The man is shocked and says that he can explain.
Just then, the Fat Controller pulls up urgently in his car. Edward tells the Fat Controller proudly that he has caught the thief. The Fat Controller informs Edward that he has made a mistake; the man is in fact a jeweller and was collecting the items to repair them. Edward says sorry, but luckily the jeweller can see the funny side.
- This story shares a similar name to the first story of Really Useful Engines.
- In the first illustration, Edward is missing his brakepipe.
- In the second illustration, Edward's running board is black.
- In the third illustration, Emily's tender is grey and Edward's running board continues onto his tender.