yes there is and it's out now but i don't know what it's called.
No, the Key to Rondo is only the first book in a series, apparently. I searched it up in the library and a SECOND book, The Wizard of Rondo, came up! There is a second book and I have read it! I won't spoil it for you though.
Emily Rodda has wriiten two more installments set after the events in the Key to Rondo. They are : The Wizard of Rondo The Battle for Rondo
The Third book in the Ingo series is called 'The Deep'.
The third book in Cynthia Hand's Unearthly series is Boundless.
The third book in the Leviathan series is called Goliath.
The third book in the series is called A FAREWELL TO CHARMS
The third book of the Dormia series is called: The Shadow Tree.
The third book in Alyson Noel's Immortals series is called Shadowland.
Kathleen Duey is currently working on the third book in the trilogy.
No, the third book in the series is called Spell Bound.
Chains of Reaction is the name of the third book in the Perfect Chemistry series.
The third book in the series is called Small Steps.