Olivia is a small and slender tan mouse. She has rounded ears, a small white bucktooth, a dark red heart-shaped nose, pink ear innards, thin black eyebrows, brown eyes, both small hands and feet, both white underwear and socks, black Mary Jane shoes, a red hair-bow behind her left ear, a white collar with a forest green or navy blue bow, a light blue or light pink shirt, a blue or pink miniskirt with a red plaid pattern, a blue or pink coat, a blue or pink tam-o'-shanter hat with both a black or purple ribbon and brim and a red or fuchsia pom-pom on the hat, and a baby blue scarf with a red plaid pattern.
Olivia is a generally naive, astute, sweet, rambunctious, and fearless little girl. She cares for everyone, especially her father (who is her only remaining living relative, due to her mother being deceased). She's fond of fuzzy animals, particularly Toby. She becomes irritated when people say her last name wrong (as is evident when Basil gets it wrong on a multitude of occasions) and she typically tells them that her last name is Flaversham (on one occasion, with the assistance of Dr. Dawson).
Role in the film
At the beginning of the film, she is having a great time celebrating her birthday party with her father, but he was kidnapped by Fidget. She went to search for Basil, but she did not know where Baker Street was, and got lost on the way. Soon, she met a kind-hearted mouse named Dr. David Q. Dawson, who just returned home after recent military service in Afghanistan when he stumbled upon Olivia. Feeling sorry for the girl, Dawson took her to the home of Detective Basil of Baker Street, where Olivia met the housekeeper, Mrs. Judson, who welcomed her in and treated her with great love and care afterwards, acting as somewhat of a mother towards her (which was, no doubt, a new experience for Olivia, since she never got to know her mother). Soon enough, Basil came back to his home, where he was, at first, uninterested in Olivia's case. However, upon her mentioning of her father having been taken by Fidget, Basil saw the case as a chance to catch his arch-nemesis Professor Ratigan at long last.
After telling Basil the story of the kidnapping in exact detail, it was apparent to Basil that Ratigan had something big planned. As Basil began to ponder what Ratigan would need a toymaker for, Fidget appeared outside Basil's window, prompting Olivia to scream in alarm. As Basil and Dr. Dawson rushed outside to investigate, Mrs. Judson comforted the scared Olivia. Shortly, the duo returned with plans to hunt down the kidnapper with the assistance from Basil's friend, Toby. Olivia wanted to come with Basil and Dr. Dawson, but Basil wouldn't accept it, saying "this is certainly no place for children". Olivia, however, was allowed to come along (for reasons unknown). When Olivia found out that Toby was a dog, she was, at first, alarmed, but she quickly became friends with the pooch after giving him one of Mrs. Judson's cheese crumpets. The group journeyed to a local toy store afterwards, where Fidget (who left his hat when he fled from Basil's home) was collecting toy soldier uniforms for Ratigan's sinister plot. During the trip through the toy store, Olivia was ambushed by Fidget, who quickly spirited her away to Ratigan`s lair. Then, all of a sudden, she remains captured for a decent portion of the movie up to the point when Basil and Dr. Dawson come to free her. They succeed in doing so after they get away from Ratigan's death machine.
Olivia, Basil and Dr. Dawson (after departing a picture for Ratigan to remember them by) then hurried on to Buckingham Palace, where they rescued the Queen from being devoured by Ratigan's pet cat Felicia, and then Mr. Flaversham from Ratigan's goons. Unfortunately, Fidget broke free of his bonds and Olivia found herself kidnapped soon again. She was thrown into Ratigan's blimp, which was pursued by a makeshift balloon that Basil, Dr. Dawson and Mr. Flaversham made out of some balloons and the Union Jack shortly.
The chase ended when Ratigan's blimp crashed into the Big Ben clock tower, where Ratigan threw Olivia into the gears of Big Ben, hoping to rid himself of her. Basil hurriedly returned Olivia to her father, but Basil wouldn't get away so quickly due to Dawson unable to move his dirigible too very close for Hiram to reach Olivia. A battle waged on the hands of Big Ben sent Ratigan plummeting to his doom. Olivia believed that Basil, too, perished (Ratigan having tried to drop Basil several stories to his doom) begins to cry softly with her father comforting her, while Dawson looks on with worried expression until he was revealed to have survived by using a piece of the eliminated dirigible. Olivia, having been reunited with her father, left after saying her goodbyes to Basil and Dr. Dawson (which occurred near the end of the movie).