The character that you're thinking of is Jacen Solo.
While on a tour of Lando Calrissian's GemDiver Station, Jacen, Jaina,
Lowbacca, and Em Teedee are caught in the middle of an Imperial raid
and kidnapped. After being informed of what happened by Lando, Luke
Skywalker embarks upon a rescue mission in search of the missing Jedi
trainees. Feeling guilty because she was not with her friends and
therefore could not help them, Tenel Ka accompanies him.
And of course, there is a "Shadow Academy":
Meanwhile, aboard an assault shuttle that figured prominently in the
attack on GemDiver Station, the twins and Lowbacca meet Tamith Kai,
the woman who led the attack. The students learn from her that their
destination is the "Shadow Academy" where they will be trained to use
the dark side of the Force in the service of the Second Imperium. Once
they arrive at their destination, Brakiss, one of Luke's former
students and the headmaster of the Shadow Academy greets them and
reiterates most of what Tamith Kai told them. Jacen, Jaina and
Lowbacca are then confined to their own separate cells.