Award-winning filmmaker Robb Leech attempts to discover what changed his stepbrother Richard Dart -- the subject of his acclaimed documentary "My Brother the Jihadist" -- from a radical convert to a dangerous convicted terrorist.

Dart, now known as Salahuddin al-Britani, received a six-year jail sentence in April 2013 for preparing for acts of terrorism. Having previously sought to understand what made Dart reject everything his family and country stood for, Leech now wants to know what, if anything, could have kept him from this fate.

Leech's journey takes him from London to known international hotbeds of Islamic radicalism, but his personal investigation starts with Anjem Choudary, the controversial cleric who led Dart's conversion to radical Islam.