I read "Murder in the Forum" because it is a murder mystery set in Roman Britain, one of those places/times I would love to time-travel to. This is the third in the Libertus Mystery of Roman Britain series. I have not read others in the series.
"Murder in the Forum" is a serviceable mystery which follows all the rules of mystery writing. Libertus, our detective, is a freed slave, born a Celt, who has been granted Roman citizenship. He has the nominal job of being a tile artisan, but in real terms he is the go-fer for Marcus Aurelius Septimus, the top guy in Glevum (Gloucester). If something happens that needs to be investigated, Libertus is given the task. He is assisted by his slave Junio, who is pretty bright too.
When Perennis Felix, a very unpleasant Roman who bears a passing resemblance to Jabba the Hutt, appears in Glevum, he demands attention be paid. He is a close friend of Emperor Commodus back in Rome. (Commodus is the Emperor in the movie Gladiator--in other words, not a nice guy.) A banquet attended by everyone who is anyone in Glevum is held to honor Felix. When he suddenly chokes on a nut and dies at the table, it is first considered an accident. But Libertus soon has suspicions that someone wanted Felix dead. There are plenty of suspects to spare. Marcus, who has recently married, is distracted, and hands the investigation off to Libertus.
The rest of the book follows Libertus as he follows clues and red herrings. It involves a tricky explanation of a potential coup that does not quite come together. I had the feeling as I finished the book that it could probably have been set in almost any historical period. Although the characters are dressed like residents of Roman Britain, we don't really find out what makes them different from us.
The book has a map of Roman Britain (not terribly detailed). It could have used a map of Glevum too, to help make sense of the trotting back and forth that Libertus does. There are some very useful explanations of life in Roman Britain, particularly about funeral rites. I would actually give it a 3.5 rating. It didn't rise to the level of a 4. One failing in the writing was the tendency to tell, not show.