Seven Keys to Baldpate
The magician shows a number of keys, demonstrating that one will open the lock. The keys are mixed up in a bag and various spectators take out a key at random, leaving the last one for the magician. It turns out that the magician has the only key that will open the lock. From the writing on an envelope with this effect, John Davenport believes that it was a trick that came from Maskelynes. The writing is the same as was found on other items from Maskelynes. Presumably they came to the Davenport family when it bought the assets of the Maskelyne business in 1935.