Robbie Flint

 was Agent Spark. Doctor Schwartzmann released him from prison for him to work as an agent as he was an explosive expert. He was sent to Cambridge to blow up a factory. He was a double agent, Agent Criss-Cross, but was eventually revealed to be working with the Waveform with the intent of taking over what was left of humanity after the Waveform had used most of the human race as resources in their own war. After the Doctor trapped the Waveform in a new code, the Waveform absorbed Flint into themselves while trying to decode the new message. (AUDIO: Criss-Cross)