Nemesis, By Lindsey Davis<br />Falco: The Official Companion, By Lindsey Davis

Marcus Didius Falco, that light-footed private eye who makes his chancy way through the patrician villas and noxious alleyways of ancient Rome, first saw the light of day in 1989, in The Silver Pigs, where he ventured to that mist-ridden offshore island of Britannia. The ingredients of the Falco series were established right at the start: as well as convincing historical detail, the novels include surprising murders, a good deal of cynical joshing on the part of the ancient gumsandal and a bold, independent woman who manages to keep him on some sort of rein. When the series started, Falco was unique in detective fiction, but as the books gathered fans, other authors tried their hands at the classical setting.

Nemesis, Falco's 20th adventure, does have a deeper undercurrent than previous books. His father, Geminus, shady dealer in works of art, had a role in Alexandria, when Falco took a holiday in that glamorous Egyptian city and clashed spectacularly with Sobek, the giant Nile crocodile.

Now Geminus has died and Falco has inherited his motley estate, including slaves and dodgy sculptures. But just as Falco is about to become rich, a technicality of Roman law presents nail-biting suspense. Geminus had taken up with a snake dancer (Davis apparently consulted London Zoo for information). Now she is pregnant, and if the child is a boy, Falco will have to share the estate with him.

Tracing a couple who have been supplying fakes to Geminus, Falco gets on the trail of a hideously dysfunctional family, psychopathic serial killers. He tracks them down to their lair deep in the Pontine Marshes – not far from Rome, but its denizens, runaways and desperate criminals, might be living on a different planet. Here, Falco is the ultimate urban man, as alien to the landscape as Chandler's Philip Marlowe might be in deepest Oklahoma.

The sleuthing is blocked by the official Roman Chief Spy, Anacrites, who hides some dark secret, but assisted by the solid person of Falco's old pal, Petronius: a low-paid member of the "vigiles". Falco's family play a far deeper role than usual: his baby son has just died and been cremated on the same pyre as his grandfather.

Anxiety about his bereaved wife underlies Falco's journey into evil. This darker edge to the book is reflected in other issues: life for slaves inherited like pieces of furniture, the ubiquitous use of torture - even Falco is tempted. Davis described the novels as "picaresque Roman soap opera", but Nemesis is much more than this. The plot dashes along, springing surprises with her usual skill, and Falco retains his sharp and witty tongue, but the novel is strengthened by deeper reflections of the harsh realities of ancient Rome.

Those realities, like everything in Davis's Roman history, are pragmatically researched. She has read the books and "walked the ground", including a perilous descent into the Cloaca Maxima. Falco, the Official Companion is a most readable mine of information about the urbs, as well as including all our hero's various itineraries around the empire. Browsing reveals fascinating entries under such headings as Law and Order, The Sacred Geese and Contraception.

It also includes interesting personal information in which a very private writer discloses much about the way she works and her early, difficult home life. Not just for Falco fans, the book has excellent maps of Rome and would make an entertaining holiday companion through mean streets and grand ones.