Mothwing of RiverClan is a small, dark, long-furred, golden she-cat with brilliant amber eyes. In The Sight, she first appears when she and Willowpaw arrive in ThunderClan camp. Willowpaw had gotten a dream from StarClan, and Mothwing wanted Leafpool to help interpret it. Mothwing said that she wanted Leafpool's opinion. She goes into Leafpool's den and soon comes out. Hollykit asks Willowpaw lots of questions about what happened, but the two RiverClan cats leave, unaware that they have inspired Hollykit to become a medicine cat. Willowpaw later sees Hollypaw at a Gathering, and congratulates her on being a medicine cat apprentice.

At the half-moon meeting of the medicine cats, Jaypaw wanders into Willowpaw's dream. He sees that Mudfur, the former medicine cat, delivers a message to Willowpaw about Twoleg kits trying to block the river that feeds the Clan.. Jaypaw is confused that Mudfur isn't telling Mothwing. He travels to Mothwing's dream and finds that she is dreaming normally. Jaypaw returns to his dream and Yellowfang visits him. Jaypaw asks about Mothwing, but Yellowfang merely scolds him for his curiosity and Jaypaw is woken up by Leafpool. Mothwing wakes up as though she has rested and leaves with Willowpaw. Before she does, Mothwing asks how Jaypaw's training is going. Jaypaw replies that the best part of it is communicating with StarClan. She changes the subject and asks him about who he's treated. He says Stormfur, and how he can't get the medicine to stay on. Mothwing suggests covering the wound with catchweed. Jaypaw thanks her and asks if she got the advice from StarClan. Sher ignores him and runs off to catch up with Willowpaw.

Later, Weaselfur and Kestrelpaw visit ThunderClan, asking for catmint to treat greencough. Jaypaw persuades Leafpool to ask Mothwing, and Leafpool returns with bundles of catmint.

In Dark River, Mothwing is sitting with Leafpool and Barkface at the Gathering. Mothwing chats with Leafpool, asking if Mousefur has recovered from greencough. Jaypaw attempts to read her mind to see what's wrong with RiverClan, but Mothwing protects her mind so the young apprentice can't read it.

At the half-moon meeting, sneaky Jaypaw travels into Willowpaw's dream to see what's wrong, and finds that RiverClan is slowly losing their home to Twolegs. He tells Leafpool what he saw. Leafpool goes to wake Mothwing, saying that they must go home.

Hollypaw is worried that RiverClan, while the Twoleg kits are blocking their river, will move into WindClan territory and start a fight. Annoyed that no one is doing anything, she travels across the ice to RiverClan's temporary home, where she meets Mothwing treating Icewing's kit's sore pads from stepping on needles. Mothwing later allows Willowpaw and Hollypaw to visit the old RiverClan camp.

In Outcast, Mothwing doesn't come to the Gathering. Willowpaw says it's because she's treating an infected bee sting, but Jaypaw believes that it's an excuse for her not believing in StarClan.

In Eclipse, Mothwing gives Willowpaw her full name, Willowshine. She is rather reluctant to do so, since she doesn't believe in StarClan.