Summary:

On December 16th, 1991 Howard and Maria Stark were killed in a tragic car accident. Or at least that's what their son and the world is left to believe. 25 years later, Helmut Zemo lures Tony, Steve and Bucky into a Siberian Hydra base to reunite a family...and use The Winter Soldier to destroy it once and for all.

OR

Howard and Maria were kidnapped by The Winter Soldier and forced to work for Hydra. Through a turn of events they are reunited with Tony, and Howard sets out to make good on the promise he made to himself when he was captured...to begin the long road of making amends with his son.