The Spectral City series:
The Spectral City
A Sanctuary of Spirits
A Summoning of Souls
The Magic Most Foul trilogy
Darker Still
The Twisted Tragedy of Miss Natalie Stewart
The Double Life of Incorporate Things
The Strangely Beautiful saga:
Strangely Beautiful
Perilous Prophecy
Miss Violet and the Great War
The Eterna Files trilogy:
The Eterna Files
Eterna and Omega
The Eterna Solution