The Gray Sisters were three minor characters in the original myth of Perseus. At one point of his journey, Perseus traveled to see the Graeae (The Gray Sisters) who knew everything. He needed the location of Medusa as he had promised the king of his island the head as a present. When he got there however, the sisters were absolutely horrified when he asked for the information. Finally he got so annoyed with them that he whacked the sister with the eye ball and yanked out the tooth. They begged for the tooth and eye back, but Perseus stood his ground. Moaning, they told him the location of Medusa, as well as three items he needed to defeat her, the shield of Athena, the winged sandals of Hermes, and the helm of Hades.
Annabeth hails the Gray Sisters' service when she, Percy, and Tyson are running from the authorities after Percy is blamed for torching the school gym at Meriwether Prep, the result of an attack by Laistrygonian Giants. Annabeth took Percy and Tyson to the road and took out a Golden Drachma and tossed it into the road after calling forth the Chariot of Damnation. A few moments later, a taxi that looked as if it were made from smoke appeared from the ground and the trio climbed into the taxi. The drivers of the taxi reveal themselves to be the Gray Sisters and at first refuse to take Tyson (as they do not accept cyclopes), but Annabeth promises extra pay on arrival.
After agreeing to take them, the Gray Sister in the driver's seat hit the gas, which forced Percy's head to slam against the headrest. As they rounded a corner, it is quickly learned that Wasp, the driver did not have the eye shared between them as Tempest, the sister in the middle yells as they were about to hit something. Meanwhile, Anger asked for the tooth so she could bite it and make sure it was real, which lead Wasp to complain that she did it last time. The three argue over the eye as Annabeth explains that the three share an eye between them, which greatly worries Percy as the cab drives up on curbs and through red lights.
The three sisters then mentioned all the famous people they have had in their taxi, including the original Jason, but Wasp points out that that was before they even had the taxi. The three once again start fighting over the tooth and eye, but Annabeth tried to reassure Percy by calling them wise. The three agreed and began to say all the things they know, including every street in New York, the capital of Nepal, and the location Percy was looking for (a location Percy did not even know he was looking for yet). Tempest's sisters were quick to shut her up as Percy had not asked about any location and Percy kept asking what they meant. They refused, as the last time they gave out information, their eye was tossed in a lake and it took them years to find it.
As the three continued to fight for the eye, Anger gets slapped on the back and the eye came flying out and under the seat, allowing Percy to grab it. They told him to give it back while Tempest began to accelerate out of control. Percy demands the information about the location, and the three sisters' give in. They tell him 30, 31, 75, 12 which Percy did not understand. He however gave the eye to Wasp and they drop the three off at Camp Half-Blood. Later at the campfire, Percy figures out that the numbers were used for longitude and latitude, leading to the Sea of Monsters.
Gray Sisters' Eye and Tooth
The three Gray Sisters' share one tooth and one eye between them. The two items normally lead to fights between them and they normally take turns. While the tooth can be used to bite down on gold (most likely to test its' authenticity), the eye is prized as it is the only way they can see. During the time when Percy, Annabeth, and Tyson were in their cab, Tempest was the one driving, but Anger was the one with the eye. The eye is also their greatest weakness, as it has been used against them to gain information as it passes between hands.