One fan took to Reddit to figure it out, with Caroline Harker, 58, quickly revealed. They asked on the discussion forum website: 'Who played the white-haired Dr Todd in tonight's episode?' ...
They soon discovered that she was none other than Caroline Harker, who'd once been a major player in crime drama Touch of Frost. She played Hazel in the series, which had run between 1992 and 2010.