While Captain Scarlet and Spectrum defend Earth against the threat from Mars, it is found that Mysteron reconstructions are particularly vulnerable to electricity[e 5] and that they are detectable on X-rays, to which their biology is impervious.[e 5] Consequently, two anti-Mysteron devices, the "Mysteron Gun"[n 11] and the "Mysteron Detector," are developed to aid Spectrum.[e 6] A three-episode story arc charts the uncovering of a second Mysteron complex under construction on the Moon,[e 7] its destruction by Spectrum,[e 8] and efforts to negotiate with the Mysterons on Mars via a crystal power source, salvaged from the complex, which is converted into an interplanetary communication device.[e 4] A failed attempt at satellite surveillance of the Martian surface,[e 9] aborted military conferences[e 10][e 11] and the sabotaged construction of a new space fleet[e 12] hinder Spectrum's plans to return to Mars, and the organisation is unsuccessful on two occasions in apprehending Captain Black.[e 13][e 14] The penultimate episode of the series depicts a Mysteron assault on Cloudbase with the use of armed spacecraft, which is ultimately revealed to be a sunstroke-caused nightmare dreamt by Symphony Angel, one of the Angel pilots, after she is stranded in the desert following a crash of her Angel Interceptor.[e 15] The finale is a flashback episode that ends inconclusively with regards to the war between Earth and Mars and the fate of Spectrum and the Mysterons.[e 16]