Undermind

Personnel Officer Drew Heriot returns to the United Kingdom after working in Australia to discover his brother, Police Detective Frank Heriot, behaving oddly, to the distress of his sister-in-law Anne. Investigating together, they discover that a disembodied alien force is using high frequency signals to brainwash people - including Drew's brother - into committing subversive acts as a prelude to a full-scale invasion. Together, Drew and Anne battle to stop the acts of sabotage while trying to alert Britain to the danger...