A pack which includes a book of secret codes with a free invisible pen and developer to help you become the mastermind behind a whole network of secret agents. Leave your friends guessing as you find out why pig pens make great homes for messages; talk nonsense with numbers; see the light, send morse code with a torch, pass on some hot gossip without burning your fingers. Create your own crafty codes, send secret signals and learn how to write letters that mean more than they seem to.