Sheriff's look at a Roman family as the Roman's were leaving Britain. That's a solid idea - it's been done a few other times but that doesn't make it less powerful. Most of the characters are sensible middle class types - the sort often found in Sheriff works. Disappointing, there's no one on the verge of a nervous breakdown like in Journey's End. However the character of Arthur - a shrewd bandit later - is interesting.
The guts of the story concerns the attempt by the paterfamilias to persuade Arthur to help lead the fight against the marauding hordes. The Roman family have Caledonian servants who aren't exactly complex - loyal to the most part, they turn into marauding dogs in battle, and are ordered to kill the paterfamilias at the end (they don't do it out of loyalty). The romance between Gawain and the eldest daughter feels perfunctory.
There are some very effective moments: the realisation from the family that Rome has collapsed; discussing the battle and describing the Saxons as being starving; the final scene where Julian and his wife go hide out in the woods, the bandits approaching, with a plan to live, but unsure if they will survive. I liked the use of religions and the drama was effective. Not a major league work and a bit inclined to totalitarianism - it's all about getting a good leader - but effective.