"IN AN INSTANT," AIRING ON "20/20," FRIDAY, APRIL 26 ON ABC

In the moment of crisis, lives can change drastically by twists of fate and split-second decisions. "20/20" reports on surviving, from random violence and acts of terror to massive highway accidents and the madness of crowds and stampedes. "20/20" airs FRIDAY, APRIL 26 (10:01-11:00 p.m., ET) on ABC. Anchored by Elizabeth Vargas and David Muir, reports include:

· David Muir reports the latest on the Boston Terror investigation, with a focus on the newly emergent heroes and survivors who came face to face with the suspects.

· "20/20" explores the phenomena of "crowd think" and the herd mentality of stampedes, where individuals forget logical thinking and instead follow everyone else -- even if it's clearly not the right thing to do. Matt Gutman reports.

· Matt and Catie Stegmoyer and their two children were driving along a Texas highway last Thanksgiving when they found themselves in the middle of a deadly 118 vehicle pileup. But the Stegmoyers were able to walk away unscathed largely because they ignored conventional wisdom about what to do in a traffic accident. John Qui�ones reports.

· What makes a difference between life and death when there is an active shooter in the office? Elizabeth Vargas speaks with workplace shooting survivors and a law enforcement official who demonstrates what to do.

· Jay Schadler reports on "The Third Man Factor" - in which survivors of terror attacks, natural disasters and other near-death experiences tell nearly identical tales of a tangible, corporeal presence instructing them to keep calm and providing direction on how to get out alive. Many believe it's a supernatural phenomenon, but author John Geiger believes our mind literally splits in two - the emotional side that panics and the rational side that thinks through the fateful decisions.

· Amputee college soccer player Bree McMahon shares her inspiring story of recovery, and "20/20" is with her as she visits Boston to support the amputee victims whose lives changed in an instant on that fateful day. Deborah Roberts reports.

David Sloan is the executive producer of "20/20."