The Three Investigators and the Invisible Enemy

The Three ??? take "their" eccentric grandfather on a cross-country trip. But very soon the vacation turns into an exciting adventure. Who is the invisible pursuer who is so relentlessly on their trail? What is a wild horde of motorcyclists up to? Why are so many people suddenly interested in Bob's camera? When the situation escalates, the detective trio decides to involve the FBI in New York and set a trap. Will the invisible opponent take the bait?

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