The series deals with an advanced civilization that is able to travel between parallel universes with alternate histories, and uses that ability to trade for goods and services that its own, exhausted Earth cannot provide.
The Reader's Guide to Twentieth-Century Science Fiction notes that, as in most of Piper's stories, the Paratime plots nearly all "rely on the self-sufficient human.
The Dwarma sector is one where paratime travel was never discovered, and the Martian colonists settled down into a subsistence agriculture economy to survive.
One major event people remembered for years is when a farmer and trader contradicted themselves on the price of a pig; they raised their voices and shouted at each other.
Verkan Vall and Hadron Dalla were planning a vacation in the Dwarma Sector when it was interrupted by the discovering of a paratemporal slave-trading ring in Time Crime.
The Jak-Hakka civilization follows an ideology of "Dictatorship of the Chosen," it has been used as an example of political structures the Home Timeline wishes to avoid.
Third Level timelines, as Piper described them, were "A few survivors—a shipload or so—were left to shift for themselves while the parent civilization on Mars died out.
Fifth level Neanderthal man exists in a Stone Age culture having evolved on Earth independently, but never advanced.
Sometimes they stumble out of the conveyor onto another timeline: this could have happened to British diplomat Benjamin Bathurst in He Walked Around the Horses (Note: This "could" is almost a certainty since the details of the story of such an occurrence that Tortha Karf tells in Police Operation match exactly the events in this story) or to the stranger on the train in Crossroads of Destiny as it did to Pennsylvania State Police officer Calvin Morrison in Lord Kalvan of Otherwhen.
Many of the inhabitants of the Service Sector, as well as servants and low-status workers in Home Timeline, are Fourth Level tribesmen from primitive cultures who are recruited by the tribe to work.
Paratime Police officers are authorized to use extrajudiciary means, such as assassination, of both Home Time residents or outtimes, to protect the secret if necessary.
Verkan Vall was born on the island of Nerros (Cuba) in the Home Timeline some time in the late 1800s; in Last Enemy, he noted he was eighty when he and Dalla Hadron were first married.
He serves as a general troubleshooter for Chief Tortha Karf and is assigned to cases that require special attention from the Paratime Police.
In Police Operation, he has to hunt down a Venusian night-hound that escaped onto our timeline; in Temple Trouble, he must rescue Home Level paratimers from torture and execution; in Last Enemy, he must locate researcher Hadron Dalla; and in Time Crime, he is in charge of an investigation to track down a large criminal organization of slave traders.
By the time of Great Kings' War, Vall has taken over as Chief of the Paratime Police, replacing the newly retired Tortha Karff.
Dalla traveled to the Akor-Neb sector to continue research, where she discovered evidence that human consciousness survives the body and reincarnation is a scientific fact; this research led to a major upset of Akor-Neb politics and societal structure, and forced Verkan Vall to retrieve her lest the Paratime Secret be disclosed (see Last Enemy).
Dalla goes with Vall to the kingdom of Hos-Hostigos in Lord Kalvan of Otherwhen, serving as a second pair of eyes and a companion to Princess Rylla, who becomes Morrison's wife.
This disturbs Vall a little bit; he regards the two women as two identical sticks of dynamite, believing that whatever sort of trouble one of them didn't think of, the other would.
Karf comes from a family of Paratime Police; his grandfather had problems with the Spanish Inquisition on the Europo-American line.
As a member of the Paratime Police, Karf inadvertently picked up Benjamin Bathurst, who was shot by local authorities before he could be recovered.
See "He Walked Around The Horses" for the details of what happened to Benjamin Bathurst from the viewpoint of the inhabitants of the timeline he was transported to.
Karf owns the island Sicily, including a farm, on one Fifth Level timeline where goes for recreation and where he plans to retire.
Deputy Sub-Chief of the Esaron Sector, discovered the Organization inter temporal slave trading activities while on detached duty working as a Guard Captain for Consolidated Outtime Foodstuffs Company under the cover name Kiro Soran.
Other works influenced heavily by Piper's Paratime include Harry Turtledove's Crosstime Traffic series, the G.O.D., Inc. trilogy by Jack Chalker, Michael Kurland's Perchance (first volume of the not-yet-continued Elsewhen series), Michael McCollum's A Greater Infinity, Richard C. Meredith's Timeliner Trilogy, Charlie Stross’s The Merchant Princes series,[4] and the GURPS Infinite Worlds role-playing game setting.