The Secrets & Spies sub-series revolves around the theme of sending secret messages via darts and "invisible ink", which is really blue ink. The Message Darts themselves are mostly white with red dots everywhere, which will make the marker hard to read when a message is written on it. The message is read by the use of a message decoder: a clear, red tube-like device which shows the message by canceling the red spots on the dart, which reveals the blue. Some blasters have red barrels or sections which show the message while the dart is loading in the blaster.
The Secrets & Spies sub-series was announced at the 2014 New York Toy Fair.