Unforgotten season four is set to hit our screens on Monday night, and see Nicola Walker return to her role as the one and only DCI Cassie Stuart. 

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However, while in previous seasons, Cassie has been hard at work on a new case, the new season opens with her off from work, and reluctant to return to her role as detective chief inspector. So what happened to her at the end of season three? Remind yourself here...