Filmmaker Doug Block had every reason to believe his parent's 54-year marriage was a good one. So he isn't prepared when, just a few months after his mothers' unexpected death, his 83-year old father, Mike, phones to announce that he's moving to Florida to live with "Kitty", his secretary from 40 years before. Always close to his mother and equally distant from his father, he's stunned and suspicious. When Mike and Kitty marry and sell the longtime family home, Doug returns to suburban Long Island with camera in hand for one last visit. And there, among the lifetime of memories being packed away forever, he discovers 3 large boxes filled with his moms' daily diaries going back well over 35 years. Realizing he has only a few short weeks before the movers come and his dad will be gone for good, the veteran documentarian sticks around, determined to investigate the mystery of his parents' marriage. Through increasingly candid conversations with family members and friends, and constantly surprising diary revelations, Doug finally comes to peace with two parents who are far more complex and troubled than he ever imagined. Both unexpectedly funny and heartbreaking, 51 BIRCH STREET is the first-person account of Block's unpredictable journey through a whirlwind of dramatic life-changing events: the death of his mother, the uncovering of decades of family secrets, and the ensuing reconciliation with his father. What begins as his own intimate, autobiographical story, soon evolves into a broader meditation on the universal themes of love, marriage, fidelity and the mystery of family. 51 BIRCH STREET spans 60 years and 3 generations, and weaves together hundreds of faded snapshots, 8mm home movies and two decades of verité footage. The result is a timeless tale of what can happen when our most fundamental assumptions about family are suddenly called into question.