Following the political assassination of Omar Tariq, a Balkan minister, Darien is summoned to help find the sniper who killed him. The problem is that the only eyewitness is Jessica, an 8-year-old girl. To try to get information from her, Darien must masquerade as her invisible friend "Ralph," which initially he is able to do successfully.
Darien earns Jessica's trust, but things start to go wrong when Darien's invisibility wears off unexpectedly and he appears in front of a horrified Jessica. He is forced to re-establish a relationship with the scared girl, posing as a now-visible Ralph.
By the time Darien finally wins back Jessica's trust, the sniper is hot on their trail and trying to eliminate them both. After a few close calls, Jessica is able to help Darien and Hobbes determine that the sniper is an American, so the assassination was probably an inside job.
Fawkes and Hobbes' search takes them deep into the ranks of the FBI, which also is handling an investigation into the assassination. With Jessica's help, the sniper is identified and brought to justice.