Leaf is a friend of Arthur's from Earth. She was introduced in Mister Monday as one of the people who helped him during his asthma attack. She can also see the Fetchers. She aids Arthur in Grim Tuesday by helping him banish a Scoucher, a monster with razor sharp tentacles.
From and during Drowned Wednesday, she begins to play a larger role in the series. She is visiting Arthur in the hospital when they are taken to the House via the Border Sea. One of Drowned Wednesday's ships rescues Leaf instead of Arthur, whom they were ordered to find; Leaf spends the bulk of the book on this ship, which is called the Flying Mantis. This changes when the ship is captured by the pirate Elishar Feverfew (who once was a mortal but has been affected by Nothing). She becomes an unwilling informant to Feverfew, only to later kick his detached head into a Nothing-contaminated lake of mud, thus destroying him.
In Sir Thursday, Leaf returns to Earth, and aids Arthur by banishing the Skinless Boy. She succeeds, allowing Arthur to return to Earth, should he choose to do so. At the end of the book Leaf is told that she is at a hospital run by Lady Friday.
In Lady Friday, Friday kidnaps Leaf, hoping to use her as collateral, a hostage, or bargaining counter in case Friday's plan went awry. Leaf works to escape Friday's retreat in the Secondary Realms, but is not successful until the arrival of Arthur and the Mariner, who find her only due to her attempts to contact Doctor Scamandros.
In Superior Saturday, Leaf returns with Arthur to the Hospital, helping to deliver the sleeping patients back to their beds. They meet Martine, the cleaner whom Leaf met in Lady Friday. When Arthur discovers that the area is going to be bombed by the army (under the command of General Pravuil, who is a spy for the Morrow Days and also appears in Mister Monday and Sir Thursday), he freezes time within the hospital, using the Fifth Key, and returns to the house, leaving Leaf, Martine and the sleepers frozen. Leaf and Martine awaken as time begins to slowly return to normal. It is only a few minutes to midnight, but time has not completely unfrozen and is going very slowly. Leaf asks Martine if there are any shelters where they can stay safe during the bombing, and discovers that there is an old building at the back which contains an Operating Theatre which used to be a World War II bomb shelter, large enough to hold most of the sleepers. Leaf and Martine struggle to move as many sleepers to an the Operating Theatre as possible before the bomb hits. At the end of the book, as they carry the last of the sleepers they have managed to rescue (although there are still some outside) into the theatre, insulation falls down from the roof, indicating that the bomb has struck.
During Lord Sunday, Leaf finds the area outside the hospital is devastated and possibly radioactive. She dons a set of clothing covering every inch of her body (so as not to come in contact with any radioactive particles) and goes to a military encampment that is supposed to cater for those in the bombed area and give them radiation suits, food and anti-radiation drugs. When she asks for supplies for the all of the surviving sleepers, herself, and Martine she is discovers that the hospital is not on the army's maps and is not thought to exist. Leaf protests that it does exist, eliciting some cheers from the surrounding queue, and meets Arthur's older brother, Erazmuz, who is part of the rescue operations. Erazmuz says they need to see if the hospital is there to verify its existence, in case it is all a hoax. Leaf is then given an anti-radiation drug and decontaminated before leading Erazmuz and some of his troops to the hospital. Martine rushes out, crying about a creature inside the building. Erazmuz has her taken away to be decontaminated, while he, Leaf and a female soldier named Chen explore the building. While they are in the building, Leaf is captured by Sunday's Dusk, also known as the Reaper, who threatens to unleash a plant-like creature called a Beastwort (the creature Martine saw) on her human friends if she does not come with him. Leaf goes with him, telling Erazmuz and Chen to take care of the sleepers as she goes. The Reaper leaves the Beastwort behind, to remind Leaf not to cause trouble on the way to and in the Incomparable Gardens, as the Beastwort will then attack. On the way to the Incomparable Gardens, Leaf and the Reaper pass through the Front Door to aid the Lieutenant Keeper. As the Keeper dies, he gives his sword, and his duties as Lieutenant Keeper, to Leaf, who is forced to hold the Front Door against attacking Nithlings.
Leaf is forced to protect the Front door. She finds that she can now identify portals into the Secondary Realms using the sword. She manages to partially force her way through the earth portal, but is stopped from venturing very far by the sword, which seems to have a connection to the Front Door. She manages to grab the Beastwort's lead, binding it to her will, and goes back into the Front Door, telling Erazmuz and Chen to take care of the sleepers. Inside the Front Door, she manages to get through a portal into the Middle House with the Beastwort (which she names Daisy) but finds the sword stuck again. Dame Primus uses her power to allow Leaf to move the sword, but cannot (or will not) remove the post of Lieutenant Keeper from Leaf. She instead charges Leaf to accompany an army to the Incomparable Gardens to attack Lord Sunday. While battling Newniths on Saturday's Tower when trying to restore enough elevators to fit in the army, Leaf loses the sword. It is instead picked up by Fred Initial Numbers Gold, who then becomes Lieutenant Keeper in her place. Leaf still has Daisy (who, it is proved, is now loyal to her even without her holding its leash) and the two are carried up to the Incomparable Gardens in a transport sling by a fleet of Borderers. However, in the Gardens, the sling falls apart and Leaf is separated from Daisy (who falls in a lake but is said to probably survive). Suzy takes her to the Elysium, where Arthur takes the seventh Key and frees Part Seven of the will. Then Dame Primus combines with the Will, and Nothing breaks in.
Arthur then becomes the New Architect. He also separates part of himself to live out the normal life he wanted to have while the original Arthur fulfills the duties of the New Architect. The New Architect then saves (or recreates) Leaf, and she returns to Earth with the human Arthur.