Feel the Fear (Ruby Redfort Book 4)

Ruby Redfort: Undercover agent, code-cracker and thirteen-year-old genius. The fourth book in the scarily awesome Ruby Redfort series, by multi-million-copy bestselling author Lauren Child. This time Ruby must pit her wits against a seemingly invisible foe. How do you set your sights on catching a light-fingered villain if you can't even see him...?