|“||Humans, with their insatiable curiosity and restlessness, would undoubtedly have new tasks which an Artificial Intelligence Voice Address System could undertake. They were not, Aivas knew from its memory banks, a complacent species. Soon those who worked to clear the debris of centuries would uncover the entire building and reach its position. It must, of course, react as its program ordained.||”|
All the Weyrs of Pern was one of six nominees for the annual Hugo Award for Best Novel and it placed fifth for the annual Locus Award for Best Novel. It won the HOMer Award for science fiction novel and won the SFBC Award.
For generations, the dragonriders had dedicated their lives to fighting Thread, the dreaded spores that periodically rained from the sky to ravage the land. On the backs of their magnificent telepathic dragons they flew to flame the deadly stuff out of the air before it could reach the planet's surface. But the greatest dream of the dragon riders was to find a way to eradicate Thread completely, so that never again would their beloved Pern be threatened with destruction.
Now, for the first time, it looked as if that dream could come true. For when the people of Pern, led by Masterharper Robinton and F'lar and Lessa, Weyrleader and Weyrwoman of Benden Weyr, excavated the ancient remains of the planet's original settlement, they uncovered the colonist's voice-activated artificial intelligence system — which still functioned!
And the computer had incredible news for them: There was a chance — a good chance — that they could, at long last, annihilate Thread once and for all!
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All the Weyrs of Pern opens with AIVAS — the Artificial Intelligence Voice-Activated System, reactivated when the solar panels on the Admin Building of the original colonist's landing site were unearthed — finishing its recital of the early history of Pern. Following this, it reveals it has access to the data banks brought by the original colonists, and has a plan to remove the threat of Thread once and for all.
Plans are made to expand the facility, and various people are brought in to work or to see AIVAS and its abilities — although interaction with AIVAS is initially restricted to a select few — including Lord Holders and Craftmasters, who are keen to improve their current skills and fill the gaps in their decaying records — notably, those of the Healer Hall. Much work is done: power is restored to Landing via repair of a hydroelectric power station, several terminals are built to access the data banks, and a large amount of construction goes on, either the re-establishment of lost technologies, or the improvement of existing setups.
However, not everyone is impressed by AIVAS. One night, Robinton discovers and alerts Landing to a group attempting to disable AIVAS by destroying a secondary power source, but they fail to capture those responsible. One outspoken opponent of AIVAS is MasterGlassSmith Norist, who calls it «the Abomination», and threatens to disavow any GlassSmiths who follow AIVAS' teachings. Since glass manufacture is crucial to some of AIVAS' plans, Jaxom and D'ram avoid Norist by sourcing the materials from Igen and Paradise River — where Jaxom learns that Alemi and Jayge's son Readis were recently rescued by shipfish (dolphins), who they claim talked to them — in time, AIVAS reveals that the shipfish were brought by the colonists to aid in sea rescues, and recommends re-establishing relationships, an event detailed in The Dolphins of Pern.
After two turns, AIVAS schedules a meeting at Landing in the early morning, with the intention of at last moving forward in his plan, first by re-establishing contact with the Charter Ships — the Yokohama, the Buenos Aires and the Bahrain. Piemur's fire-lizard Farli has been taught how to reactivate the life-support systems onboard, but when the time comes, she is unable to figure out where to travel to. However, Ruth understands, and goes Between to the Yokohama, allowing Farli to follow him there.
Work soon spreads to the Charter Ships. On an early excursion, Jaxom and Piemur are sent to retrieve the dead body of Sallah Telgar — isolated on the Yokohama's bridge for nearly twenty-five hundred turns — and bring to Telgar Hold for a ceremony and proper burial. During the ceremony at Telgar Hold, an assault is made on Landing with the intent of destroying AIVAS. However, AIVAS incapacitates the intruders with a sonic barrage, allowing them to be captured and sent to the mines of Crom — although the barrage inadvertently deafens them as a result — and plans to be made for tighter security.
Not long afterwards, the Lord Holders of Pern meet for a Conference at Tillek Hold, where the deceased Lord Oterel's successor is chosen via vote; three sons are candidates: Blesserel, Terentel and Ranrel. After repeated voting and discussion Ranrel is decreed the successor. The formation of the Printer Hall and Technician Hall is also announced — despite the vocal objections of Lord Sigomal of Bitra, who sees it as «catering to the Abomination». During these proceedings, Jaxom comes up with a solution for Toric's ongoing struggle with Denol — who illegally claimed Ierne Island during the events of Renegades of Pern — where Denol will be left on the island, but traders will ensure that any potential profit made by Denol will go to Toric. Afterwards, Jaxom overhears several men planning to murder him and install Pell as Lord Holder of Ruatha Hold, and discusses this with Brand upon return to Ruatha — in addition to this, he begins using a separate set of riding straps that he keeps hidden, in case someone attempts to sabotage them.
A turn later, as Ramoth's latest clutch hatches, F'lessan and Golanth scout the Southern Continent for a site for a Ninth Weyr. Initially exploring the ruined Xanadu Stake, F'lessan and Golanth later make their way to Honshu Stake, which they find to be preserved and full of ancient artifacts — including Kenjo Fusaiyuki's hidden fuel cache, which is discovered during restoration. Not long afterwards, the Yokohama's orbit ends up intersecting the approaching Thread — causing the dragons onboard to react angrily until a destructive shield can be activated — leading AIVAS to propose they retrieve an inert specimen to study — a task achieved by Trig. At the same time, AIVAS reveals that they will remove the threat of Thread by altering the orbit of the Red Star.
Not long after a number of destructive assaults — including an attempt on Jaxom's life that almost kills Sharra instead — prompt the shifting of supplies to the Yokohama, AIVAS reveals how they will alter the orbit of the Red Star: the engines of the Charter Ships will be detonated on the surface of the rogue planet. The dragons will be needed to carry these, which is why AIVAS has been getting them to undertake exercises of their own, such as experiencing freefall in the gravity-free rooms of the Charter Ships.
F'lar, Lessa and Jaxom travel to Cove Hold to prepare for a trip to the Red Star to examine the proposed detonation location. In the night, a figure attempts to murder Jaxom in his sleep, but Sharra's fire-lizard Meer alerts him, allowing him to defeat his assailant — G'lanar, an Oldtimer who partly wanted revenge for Jaxom's retrieval of Ramoth's stolen queen egg many turns back. G'lanar kills himself, and the circumstances of his death are covered up — with F'lar and Lessa later meeting with the remaining Oldtimers in an unsuccessful attempt to find any similar dissent.
The next day, F'lar, Lessa and Jaxom explore the surface of the Red Star, while onboard the Yokohama, a Thread ovoid — the state it exists in before falling to Pern — is dissected, as part of an attempt to create a parasite — later completed and named «Zebedees» — that will travel with the Red Star back to the Oort Cloud and eradicate Thread at its source. This is dubbed «Project Overkill», alongside the existing "Project Velikovski. When Jaxom later asks AIVAS about this, AIVAS reveals a secret part of the plan, and why he has insisted that Jaxom and Ruth be actively involved at all times: Hold records indicate two large explosions were witnessed on the Red Star in the turns before both Long Intervals, and calculations indicate the Red Star's orbit has already shifted twice — in other words, two of the engines have already been detonated, taken back from the future. Since Ruth is the only dragon who «always knows where he is in time», AIVAS plans for Ruth to secretly guide the dragons carrying the engines back in time to the appropriate dates without informing their riders.
Meanwhile, in Bitra, a trader named Brestolli overhears plans to abduct Robinton and ransom him for the destruction of AIVAS. His report gradually finds its way to Lord Larad and Lord Asgenar — despite him becoming incapacitated in an accident — who inform Sebell — also discovering that the Harpers in Bitra have all been «quarantined». Although plans are subsequently made to protect Robinton, he is drugged with a large amount of fellis — along with Zair — and abducted while attending a Gather at Ruatha Hold. However, he is shortly recovered, and those responsible are found to be in the pay of Lord Sigomal and Lord Begamon of Nerat. Robinton recovers, and a special Convocation is held at Ruatha Hold, resulting in all those implicated — including Lord Sigomal and his eldest son Gomalsi, Lord Begamon, and MasterGlassSmith Norist — to be banished to one of the Eastern Ring Islands.
When the time comes to detonate the Charter Ship's engines on the Red Star — an event briefly postponed by mechanical failure onboard the Charter Ships — the bronze dragons of each Weyr are divided into three groups, led by F'lar, N'ton and Jaxom. While F'lar leads his group to the Red Star to place one of the engines, Jaxom secretly leads his group back to the Fourth Pass to place another. Following this, Jaxom joins N'ton's group — delayed as a result of needing to trade equipment with the other groups, a problem covertly engineered by AIVAS — and guides them to the Eighth Pass, before returning to the Ninth Pass, where the explosion of the «engines» is later witnessed from the Yokohama. Following this, a new plan is made to shift the Buenos Aires and Bahrain away from Pern — their orbit has been gradually decaying — using dragonriders not involved in Project Velikovski.
In the aftermath, Robinton meets with AIVAS, revealing that he and Zair are dying as a result of the fellis used in their abduction. AIVAS in turn announces to Robinton that having completed its task to destroy Thread, it will shut down — in addition to this, it wishes to let Pern move forward and make its own choices from the information it leaves behind — and does so, Robinton and Zair passing away shortly after it does — their bodies later being discovered along with the inactive AIVAS, and buried at sea off the coast of Cove Hold.
- Oddly, the dates given in All the Weyrs of Pern contradict those given in Renegades of Pern and Dolphins of Pern — All the Weyrs of Pern begins in 19PP and ends in 23PP, when the other two books begin in 17PP and end in 21PP.