I doubt very much that anyone reading this blog is unfamiliar with the name Larry Niven. Starting in the mid-1960s, he wrote or co-authored scores of novels, mostly "hard" SF, and mostly fitting into one or more of several universes which he developed (many of the series being interlinked). His stories are always very readable, full of intriguing ideas and leavened with a sardonic sense of humour. His most famous novel must be Ringworld which emerged in 1970 and won several awards (including an informal one from me, as being one of my top three SF novels - for the record, the other two are Bester's Tiger Tiger and Herbert's Dune). As far as I can recall (I have about twenty of his books, but there are many I haven't read) all of Niven's stories are set in the future, but some are much closer to our own times than others, with the adventures limited to the Solar System. The "near future" ones are often collectively known as Tales of Known Space. Flatlander is a subset of these, with the subtitle The Collected Tales of Gil "The ARM" Hamilton. It should be noted that this collection first emerged in 1976 under the title The Long ARM of Gil Hamilton but was modified and added to in 1995, being reissued as Flatlander. This is the one I am reviewing here, with five stories which are effectively episodes in the life of Gil. For the sake of completeness I should add that, according to Wiki, another story in this series (Sacred Cow) was co-authored by Steven Barnes and published in 2022, but there seems to be some query about it. To add to the confusion, one of the stories in Flatlander - The Patchwork Girl (see below) - is also the title of another anthology which includes this story.
The world of Flatlander is one in which humanity has spread throughout the solar system, but with very different cultures: the "Belters" who normally live in the asteroid belt and make a living from mining the asteroids, the "lunies" who live on the Moon, and the "Flatlanders" who live on Earth.
Gil Hamilton was born a Flatlander but moved to the Belt to make his fortune. He loses an arm in an accident and after some months returns to Earth where replacement body parts are much cheaper. In the meantime Gil discovers that he has acquired a psi power: he retains a connection with his lost arm and can manipulate light weights with it, an ability which remains with his "ghost" arm even after he has aquired a replacement genuine item. He decides to join the United Nations Police, known as the Amalgamation of Regional Militias or ARM, which in conjunction with his psi power inevitably gave him the nickname of "Gil the ARM". It also provides the framework for these stories, which are all murder mysteries which Gil has to solve.
There is one quirk which runs through all of the societies in these stories - medical science has advanced to the point that body parts damaged by injury or disease can be replaced without risk of rejection. In fact, the demand for replacement parts is much greater than the supply. As a result, an illegal trade in body parts develops (known as "organ legging"), and in due course the legal system is changed to permit disassembling criminals for their body parts, with the offences carrying the death penalty becoming ever more trivial.
The five mysteries which Gil has to resolve are:
Death by Ecstasy in which a former mining partner of Gil's dies through "current addiction" in which an electric charge is delivered directly to the pleasure centre of the brain, so powerful that the victim starved to death - but was it suicide or murder?
The Defenseless Dead in which organ-legging and its implications are explored in depth;
ARM, in which the invention of a kind of time machine facilitates new ways of committing murder;
Patchwork Girl, in which Gil gets involved in an international conference on the moon and is faced with solving a murder which seems to have only one simple solution - but one which would result in a beautiful woman being reduced to a collection of body parts;
The Woman in Del Ray Crater, in which a long-lost body is discovered in a crater of the moon; the problems here include intense radiation from fusion power plants and the shielding technology being developed.
In an interesting Afterword, Niven comments on the problems of combining SF with a murder mystery, and how the stories came to be written.
These are all very good stories, and as a collection make a great introduction to Niven's work.