Book series by Jennifer Rowe
The Rondo series is a children's fantasy novel trilogy written by Jennifer Rowe under the pen name "Emily Rodda".
"The Key to Rondo".
"The Key to Rondo" is the first book of the "Rondo" trilogy.
Plot.
After Leo's Great Aunt Bethany dies, Leo receives a family heirloom - an elaborate and fancy music box. There are four rules to the box: 
1. Never turn the key more than three times.
2. Never wind the box when the music plays.
3. Never close the lid before the music stops.
4. Never move the box while the music is playing. 
Leo, being the predictable, responsible boy he is, never even considers breaking the rules. And if he hadn't, perhaps for the rest of his life, the music box would have remained just that - a music box. He never expected his cousin Mimi Langlander to enter the equation.
Mimi is sour, sarcastic and short-tempered; therefore it comes as no surprise to Leo that she is friendless. Even her own family can’t stand her. Things are exacerbated when Mimi, disregarding the rules, makes Leo turn the box five times. Out steps the evil Blue Queen, who introduces the kingdom of Rondo, the world inside the music box, to the Langlander cousins. The Blue Queen informs the cousins that for generations, Langlanders have traveled to Rondo using the Key of Rondo, which allows them entry to both worlds. The Blue Queen attempts to lure the Langlanders into Rondo, and when they refuse, she steals Mimi's dog Mutt back into Rondo, leaving the 'Key', a ring, behind.
Heartbroken and distressed by the loss of her dog, Mimi takes the 'Key’ and - despite Leo's warnings - enters Rondo. What Mimi doesn’t count on is Leo being dragged along into Rondo with her. As Mimi refuses to return to her world without Mutt, Leo reluctantly agrees to join Mimi in her quest to retrieve her dog. In the process, they expose several ancient secrets, defeat the Blue Queen, recover Mutt the dog, and discover the real Key; a pendant Mimi inherited from her Great Aunt Bethany. With that Key, Mimi, Leo and Mutt exchange farewells with their new friends and travel back to their world.
"The Wizard of Rondo".
"The Wizard of Rondo" is the second book in the Rondo series. It was published in 2008. It is the sequel to "The Key to Rondo" and is followed by " The Battle for Rondo"
The book's main characters are Leo and Mimi. They have a magical music box that can transport them to the world of Rondo, with the help of the key to Rondo, a medallion and necklace that contains the "hair" of the tip of the brush that painted the music box's beautiful sides as the world of Rondo's landscapes, and other than transporting one from the world and back to our own, it also gives the ability to the wearer to change everything they want to. But that power should not be misused.
Plot.
Leo and Mimi have their roles to play in the world of Rondo. They need to visit Rondo occasionally to make sure the people of the world don't find out, that they're not from there. But they still have to deal with the evil Blue Queen. And suddenly a great danger raises: the cloud palace.
They go on a quest to help find a wizard named Bing with the help of Conker and his talking duck and friend.
"The Battle for Rondo".
"The Battle for Rondo" is the third book in the Rondo series. It was published in 2009.
References.
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