After her bittersweet success in series one, Karen has been promoted to Detective Inspector and seemingly given the authority she has long been fighting for. Just as she’s getting into the swing of her powerful new role, she is assigned an infamous unsolved case that will put her under intense scrutiny; from her boss, from the media, and ultimately, from sinister forces that would rather the past stayed in the past.
　　The 1984 case of Catriona and Adam Grant has confounded investigators and intrigued the public like no other. Catriona, the charming young heiress to a vast oil fortune, and her two year old son Adam, were brutally kidnapped at gunpoint outside a fish and chip shop in Fife. The ransom notes that followed stirred up an uncontrollable press storm, but when the culprits fell silent, the police faltered, and Catriona and Adam were never seen again.
　　Now, a man’s body has been discovered, with indisputable links to the original kidnap. With the first piece of evidence in decades, Karen must assemble an unbeatable team alongside her sincere and lovable sidekick DC Jason ‘Mint’ and the brilliant – but romantically complicated – DS Phil Parhatka. With the international renown of the kidnap and the constant pressure from Catriona’s father, Sir Broderick Grant, the team take on the biggest challenge of their careers to date. As Karen delves deeper into what happened in the autumn of 1984, political grudges and painful secrets reveal themselves, and it soon becomes clear… the past is far from dead.

　　故事讲述迈尔斯把生命耗在了毫无前途的工作上，然而他的生活却因意外发现的黑暗网站而有所改变。

　　这一季对应原著小说第七部和第八部，主人公乌特雷德尝试夺回贝班堡未果，后又卷入麦西亚君位之争，并再次面对丹麦人入侵。

　　本剧改编自David Nicholls的同名畅销小说《一天》。
　　1988年7月15日，Emma Morley（安比卡·茂德 Ambika Mod 饰）和Dexter Mayhew（利奥·伍德尔 Leo Woodall 饰）迎来了自己的毕业之夜。尽管大学即将结束，不过这是两人第一次跟彼此说话，第二天早上他们便各奔东西了。第二年、第三年，以及接下来的每一年，在这平凡的一天，他们会是什么样子呢？每年的这一天，Dex和Em都大了一岁，他们见证了彼此的成长变化，经历了分分合合，体会了喜怒哀乐。