When the rain during the plum rainy season soaked the green tiles, Lin Yanzhi, a graduate student in the Department of History, was sorting out his grandfather's belongings when he accidentally discovered the copper key wrapped in a blue cloth strip in the attic. The moment the rusty lock cylinder turned, she broke into a corner sealed by time - a mysterious note was stuck on the third pane of the wooden window, fresh scratches appeared on her grandfather's notebook, and a bloody silver lock plate was hidden in the drawer of the iron cabinet.
"The third window is always open." This recurring phrase in her grandfather's diary became a puzzle that haunted her. When she was drawing a sketch on the window pane, Shen Xubai, the administrator of the ancient books department of the library, suddenly pointed out: The proportions of this window pane were surprisingly consistent with the scene sketch of a disappearance case thirty years ago.
Shen Xubai's grandfather was the person in charge of the case that year, but he resigned mysteriously after the case was concluded, leaving behind a box full of files marked with the word "Window". Two people burdened with family mysteries walked together and followed the clues in the attic: the rainy night in 1987, the fire in the supply and marketing cooperative's warehouse, the erased report records, and the unanimous "no memory" of all insiders.
With each layer of clues uncovered, new mysteries surface. What does the "moving window" in Grandpa's notebook mean? Why does the silver lock hidden in the file by Shen Xubai's grandfather fit perfectly with the lock plate in the attic drawer? When they found the real "third window" in the archives of the old city, they discovered that behind the window was not only the secret of two families spanning thirty years, but also a truth about protection and redemption buried by time - the so-called window that is always open is never an entrance to the past, but is left to the future.
