The egg sac is the young of some mysterious beast, possessed with great power to shape the world. It is about the size of a watermelon, with a jelly-like appearance and a multilobed shape, like frogspawn or a bunch of grapes. It also glows and pulses.
History and Involvement
Eastern Folly arc
The egg sac was found upon the altar of the Cathedral of the Mother-Beast by a group of youths from Blackwick. Janek Polyte took it home and attempted to keep this secret, but the information leaked as the group were making inquiries about similar occurrences. The town held a large meeting in a field to discuss what they should do.
When the date of the harvest festival abruptly changed, the egg sac was used as a prop in the mummer's play, as there was no time to create a special effect for a certain object in the script that glows and pulses; various residents realized that this object likely had been a representation of the egg sac all along. During the performance, the Harvest Queen gives it to the head miner, warning them to be careful. The miners brought the egg sac into the caves and, when they found an enormous wooden nest in there, set this up at the mine entrance with the egg inside. This somehow broke the curse upon the town.
The Candle Factory
When the egg sac is stolen from the nest, the Blackwick group is contracted to retrieve it. While half the group travels south to catch the Grand Cormorant, the other half cuts through the mines to see if it was taken that way.
The egg sac had in fact been stolen by the Toll Collectors, who had been hired by Eyes, Ears, and Mouth on behalf of Regan Alaway. Alaway had figured out that the egg could be used as a power source to provide electric light not just to his house or the town of Yellowfield, but the whole world.
When Chine, Es, Marn, and Virtue descend to the deeper levels of the Yellowfield Candle Company, they find the egg sac on a corrupted stone altar of Slumbous, pierced with various cables and powering a number of electric lightbulbs mounted on candelabras. Chine ate one of the lightbulbs, giving them a vision of the egg sac's history and future, shaped around three questions asked by Dre: "What's in the egg sac", "Can I hatch this? Or grow it, I guess", and "Can I unplug this thing?". Using this information, he was able to guide Marn to surgically disconnect the egg sac, and keep it safely.
Hark! The Citadel Beneath
After Chine's failure in Episode 21 to pass the border checks and safely enter Sapodilla, their possessions were removed and, with the exception of the egg, placed in the armory of the Interred Citadel. On being freed by his friends, Chine insisted that they must find the egg sac immediately.
Felix Hollowfield had placed the egg sac in a cage in his laboratory. After his death, Mabriella du Feza moved it to the cage under the orrery where Dyre Ode's sternum was kept. Soon before the Blackwick Group arrived, it hatched into a horrid creature described as resembling both a dolphin and a velociraptor, which then puked on Chine's shirt. They were immediately besotted and decided that their life's purpose had been to take care of this thing.
Further adventures
See the article on The Baby for continuing information.