Lucy Heap (née Gringe) is the daughter of Mr. Gringe, the Gate Keeper, and Mrs. Gringe. She has a younger brother, Rupert Gringe, who worked with Nicko Heap in Jannit Maarten's boatyard, and who, like her parents, greatly disapproved of her relationship with Simon Heap.
She fell in love with Simon Heap at the age of fourteen, when they were both at a ballroom dancing class, and they almost married when they were seventeen, They succeeded later on, finally marrying in Fyre.
She has brown hair and big brown eyes. Her hair stretches all the way down to her waist, and she almost always wears it in two plaits, with lots of ribbons braided in. She wears long dresses, often decorated with flowers she embroidered herself, and boots several sizes too big for her.
She can be very girly at times, and is known to love ribbons and pretty things. However, she can also be very tough and stubborn. Overall she is a very strong and determined character.
Lucy Gringe met Simon Heap when he sneaked away from the rest of the Heaps. They tried to get married, but the Suprieme Custodian captured Simon and interupted the wedding.
Septimus Heap met Lucy on the outside path, when she ran away from home to find Simon. Simon sent her a letter telling her to wait for him, but she was tired of waiting. She didn't know where he was, but decided to go to find him herself. She took one of her brother's paddle boats and set of toward The Port. Later on, Wolf boy found her by the river. She was very distressed because her boat was missing. Nicko Heap had been looking for it, and had found it while she was sleeping. She went to him and demanded to have it back, but he ended up giving her his boat instead. Lucy was very relieved, but tried not to show it. She knew that her boat would not have been sturdy enough to travel all the way to The Port.
She arrived at the Port late at night. The next morning she bought several pies from Maureen, the owner of the Harbor and Dock Pie Shop. Maureen saw how cold she was, and invited her to sit by the fire. Lucy ended up working in the pie shop with Maureen in exchange for a bed in the corner of the shop. She asked everyone who came to the shop if they had seen Simon, but none had. Finally she met Stanley, who, after a long while, finally agreed to take her to Simon. They left in early spring and headed toward the badlands. By late spring Lucy and Simon were reunited.
Lucy went with Simon to get a diamond ring. She got one, but she and Simon came back to the landwurm burrow to find a crowd of Things that Merrin Meredith had summonded. They also found that Sleuth was gone, and Simon decided he must find Merrin and get Sleuth back. They also found a note from him telling them that they'll never get Sleuth back. Simon was outraged, and they set out for The Castle at once.
Lucy encountered Wolf boy in the House of the Port Witch Coven. She had been kept prisoner by the witches for several days after they had captured her at the market. The witches offered her to Wolf Boy as Grim food, and he eventually accepted. It was clear that if he did not, they would just push her in anyway. The witches went upstairs for the Grim feeding, leaving Wolf Boy a small amount of time to come up with a plan. He told Lucy to scream, and while she did he fed two vampire cats to the Grim. Wolf boy cut off the tip of one of the Grim's tentacles, and then he and Lucy escaped through a hole Lucy had made in the cellar wall. When Lucy and Wolf Boy sneaked away, they were chased by the witches (who smelled the Grim blood from the tentacle Wolf Boy cut off). Simon saw them, thinking Lucy ran off with another younger man. In truth, Lucy and Wolf Boy headed into Skipper Fry's boat that just set of for CattRock Light. There they saved the life of Miarr Catt and helped him to get back his Sphere of Light. They met Septimus and others on the Isles of Syren and together they managed to trap Fry and his two servants into Cerys. She was later reunited with Simon again.
Lucy took the port barge to the castle in order to deliver wedding invitations to her and Simon's parents. Whilst at her parents' house she encountered Thunder, and she knew that Simon was in trouble. She sent him a message, but got no response.
Lucy married Simon. She was also the architect of the Alchemie Chimney.
Lucy worked as a servant to the Lady and helped prisoners escape. Her's and Simon's son, William, was being held by the Lady and with the help of Tod, Oskar, and Fergie, she successfully infiltrated the place where all the prisoners of Oraton-Marr were being held. She was reunited with William.