They initially assume they have won an advertised £1,000 cash prize for being the store's millionth customers, but instead are accused of shoplifting.
The thief brags to the Trotters that the police have nicknamed him "The Shadow" because he is a fast and quiet mover in a manner very similar to that of The Scarlet Pimpernel.
The next morning, with only half an hour to go until the safe's time lock expires, Del, Albert, Mr. Peterson and Mr. Clark awake to find Rodney tip-toeing over to reach and grab the sleeping Shadow's gun.
In order to solve their respective problems, the three planned to stage a robbery and share the £60,000 in the safe, but needed independent witnesses, so they brought the Trotters into the office after falsely accusing them of shoplifting.
Instead of going to the police, Del strikes a deal with them: they will hire Lennox as a security guard with a view to becoming head security officer when Mr. Clark retires, and when the Trotters return to the supermarket later that day (as most of the food from their original trip has gone stale), the family will be named the supermarket's millionth customers and awarded the £1,000 prize.