The Scapegoat, based on the 1957 novel by Daphne du Maurier, tells the story of John Standing and Johnny Spence, two men who are remarkably similar in appearance. Standing, an out of work teacher, and Spence, a failed businessman, (both played by Matthew Rhys) meet in a pub and Spence decides he can use the situation to his advantage: he gets Standing drunk, steals his clothes and wallet and effectively gives his life to him. Standing is awoken the next morning by Spence's chauffeur and finds himself pushed into being Johnny Spence, who turns out to be a thoroughly despicable man. His wife is so scared of him that when she breaks a special plate of his their young daughter offers to fix it so he'll be mad at her and not her mother; his sister blames him for a tragedy; his mother has a morphine addiction funded by her son and he's sleeping with his sister-in-law. Added to which, he's completely ruined his business. Standing sets about fixing things as best he can but what will happen when Spence returns to claim his life?
This only works if you can look past the three levels of implausibility it poses at the start: firstly, that two men who look so similar would meet at a moment so fortuitous to one; secondly, that the reluctant impersonator wouldn't run away the moment things became clear; thirdly, that the family wouldn't recognise the imposter. In fairness to the story it attempts to deal with the last two but not wholly successfully. However, an excellent cast makes up for any plot deficit. Aside from Matthew Rhys the cast includes Eileen Atkins as Lady Spence (the mother), Jodhi May as Blanche (the sister) and Sheridan Smith (the sister-in-law). Phoebe Nicholls also deserves a mention as housekeeper, Charlotte. They combine to make a perfectly plausible - if completely dysfunctional - family unit.
I think the length of the episode (100 minutes) suited the story. Any longer and the situation would've become ridiculous but there was enough tension in the plot to keep it going for this length of time. There are a few particularly memorable scenes but I don't want to spoil the story for anyone who doesn't know it. Worth a watch, in my opinion, but don't expect action and thrills. This is much more slow-moving and all the better for it.