Book 1- 'Sierra'.
A young man named Jeff Greene falls through a space door invented by his employer and finds himself on another world. To enable him to survive on the alien world he makes use of a machine that changes his form to that of one of the locals- half horse, half human beings called quinolans. His adventure begins when he realises that there are other beings on this world as well and that he must give himself into the care of one if he wants to stay. Within a few days he finds himself being trained as a racehorse to win a particularly important race for his new owner. He does well but his racing career is interrupted when he is seconded into the army for a special mission.


Book 2- 'Ta Ashi'.
The adventure continues in Book 2. Sierra finds that the war is not quite over for him and nor are his adventures. Before getting home and back to his life as a racehorse he finds himself travelling across Cantella, competing in an unusual sporting contest and facing both wild horses and wild animals. In his travels he is seen by Aleena, the leader of the country. She decides she must have him for her own and threatens another outbreak of war if she does not get her way. Eventually, to resolve the problem Sierra must make the decision as to whether or not he should return to Earth.


Book 3- ‘Females’.
Sierra encounters a lost black foal and plays detective to unravel its origins. After a return to his racing career he travels to Lost People Valley to solve another mystery. He finds himself acting as a trade ambassador for a while, then becomes a matchmaker. An old rival surprises him and he is preparing to race once more when a rescue and an accident change his plans.


Book 4- ‘Far Places’
Sierra travels to distant places in a search for another black horse and benin- a substance vital to his adopted country.
What he finds on the far side of the Impossible Range surprises everyone and what is lost by a member of his party will eventually send him on a shopping expedition back on Earth.

Book 5- ‘Loss’.
Sierra makes a reluctant move to a new city and an even more reluctant move into a new career as a photographer. After a search for a mate, his job takes him to the far southern regions of Zammar. After a mishap in a river he and his friend To Arvo are lost for a long while and must battle to find their way back to their home and families.


Book 6- ‘Gain’.
While working as a Troubleshooter in a dangerous undercover operation Sierra finds a friend he thought he had lost. He helps To Arvo when he has to go hunting in a most unusual location then he and his family set off on what is supposed to be a relaxing overseas holiday only to find themselves in the hands of pirates. After being delayed by a trial he enlists the help of his friends to travel across Cantella to a distant and legendary city to rescue his family. On his return to Zammar, a man he always believed to be a good friend tricks him into revealing his true origins and to taking him on a visit to Earth.


Book 7- ‘Hidden’.
A woman named Mary settles into her new life on Kalla For. Sierra wants to remain on the Larn estate to help find a treasure that is believed to be hidden there but he learns that an old friend is very sick and travels north to look for a cure for her. After falling victim to a jealous colt and battling his way out of a very tight spot he learns that the Rohn has been smitten by a Zammoran woman and is neglecting his work. With the help of To Arvo’s cousin Ey Lith, he tries to set things right but is unsuccessful. Returning to the Larn Estate he and Thax resume their hunt for the treasure.


Book 8- 'Treasure.'
While Derro Par and Alapao induct a new recruit into the Troubleshooters, Sierra helps the Rohn find a suitable wife. Gra Jon arrives in Mochock for the wedding and enlists Sierra and Thax to help him test a hot air balloon. They crash in a small town with a strange name and learn a secret about To Arvo. Meanwhile Sally is having an adventure of her own; she gets lost in the Sands and learns its secret. Naylia invades Tima Well to rescue her.
The newest member of the Troubleshooters goes hunting for gold in the Galla Luen jungle and Thax finds his treasure.


Book 9- 'Hints'.
Sierra and To Arvo go in search of a semi mythical animal, run for their lives from a pack of dules, help a man protect his land by playing the part of the Dark Lord and his companion, and follow the trail of a stolen yellow colt across Cantella only to become slaves on the estate of a madman. With any usual methods of escape not likely to result in success they try something very unusual- using food as a weapon.

Book 10- 'Clues.'
While looking for Gra Jon who is missing, Sierra and Alapao experience a strange little adventure in which they meet a very small hero. Later, while Alapao goes on a trip with two fillies, Sierra returns to Tironda to his work on the Animal Catalogue and in the course of testing a new balloon is kidnapped and taken north. To Arvo’s cousin Ey Lith, falls in love with a young man of a noble family in Shalbess. Armo Eralya is an amris and his grandmother has great plans for him... plans that do not include him marrying a Mollet girl. In order to break up the relationship she wants to bring to light old laws that she has found in an ancient book. In order to do that she accuses Regil Larn and Dana Hedra of conspiring to keep secret the treasure that was found on the Larn Estate. The pair find themselves in court. Believing the truth can be found in images from the past Sierra hurries to view the videos found in the treasure chest to see if he can find something to help. What he learns surprises everyone.


Book 11- ‘Freedom.’
In Shalbess, Aleena, the Iwah Palomar is very ill. To help cheer her up Dana tries to buy a mysterious true black horse that has been offered for sale. The problem is that he speaks a language no-one in the world can understand. Dana asks Sierra for his help but he cannot understand him either. He has a suspicion that Tanis- the black horse- may have come from a long lost civilisation on the other side of the planet but before he can go and investigate he is obliged to concentrate on his job with the Animal Catalogue project. He lives for a while in a haunted house, meets a To Arvo look alike and helps the Rohn play the part of the White Lord. Alapao and Zarshon travel around the world seeking to learn about mekon script and the origin of the quinolan species.

Book 12-‘Fables’.
Sierra and Alapao chase after a band of children who have set off on an ill conceived adventure. They meet a herd of wild horses who tell them some interesting tales that excite their curiosity about the origins of quinolans and the possible tie in with Tanis- the black horse Sierra met in Shalbess. Aleena, the Iwah Palomar is dying and no one seems to be able to help her. Dana appeals to Sierra to ask Gra Jon for help. Sierra talks to him and the man says that he does know something that will help. Although at first he is reluctant to go for it, he eventually does and his help results in some amazing revelations. Meanwhile in Zammar the Rao Se Rama are formulating plans for invasion. Sierra and Tanis get involved in a battle and Sierra learns some astonishing truths.