Marsh Ngaio. When in Rome

When in Rome is a detective novel by Ngaio Marsh; it is the twenty-sixth novel to feature Roderick Alleyn, and was first published in 1970. The novel takes place in Rome, and concerns a number of murders among a group of tourists visiting the city; much of the action takes place in the "Basilica di San Tommaso", which bears some resemblance to the Basilica of San Clemente.