A UFO evades Skydiver and lands. A Mobile closes in, and operative Clifton sees a chance to capture it intact. But shortly after he enters it, the UFO self-destructs. This is the third incident to happen like this, and Straker is called to a meeting with Sir Frederick Markham, SHADO's Whitehall liaison. Scientist Lisman has developed a remote controlled hunter-killer device called 'Tommy' for military use, but it could be used to investigate the UFOs without further loss of life. Straker is reluctant but 'Tommy' is forced on him to use.