Trial by Dragons(2016)
(The fourth book in the Warlock's Child series)
A Novella by Paul Collins and Sean McMullen
It's hard to save the world when you are in jail. Dantar and Velza, children of the warlock Calbaras, need to escape from jails six hundred miles apart to stop their father unleashing a catastrophically dangerous spell. Both will soon learn that they are not just special, they are also very dangerous.
Used availability for Paul Collins's Trial by Dragons
April 2016 : USA, Canada, UK Kindle edition