House of Marbles Invisible Ink UV Light Spy Pen, for Kids Notebooks, with Magic Secret Message Writing;

Part of our "Super Secret Spy" range this clever spy pen lets you write secret messages only revealed by the built in U.V. light! Perfect for any budding spy. Write with one end of the pen on a piece of paper. To the normal eye it will look like a blank piece of paper, then use the other end of the pen to shine the UV pen on it and the secret message is revealed.