Death on the Caldera by Emily Paxman

It's Murder on the Orient Express - with witches!

A thrilling blend of fantasy and classic murder mystery, this rollicking adventure with a wide cast of suspects is ideal for those who love both Agatha Christie and V. E. Schwab, and are drawn to stories that take place in a vivid fantasy world.

The Linde siblings-Kellen, Davina, and Morel-are anxious to return to the kingdom of Halgyr before their father dies, leaving Kellen to assume the throne as king. They book tickets on a luxury express train, expecting a swift journey home-but disaster strikes when the train engine explodes, stranding the siblings atop a caldera bubbling with volcanic magic.

The crash triggers Davina's latent witch powers, but her magic disrupts her ability to remember what she was doing when the explosion took place. While a witch would be the prime suspect for the explosion, the only ones who knew Davina might become one are her brothers-who never warned her, driving her away from them. And, to add insult to injury, somebody is bumping off the surviving train crew and passengers. But it can't be Davina, can it?

While the surviving passengers try to determine who sabotaged the engine and catch the killer, the fractured siblings attempt to stay one step ahead, concealing not only Davina's powers but their own secrets. Luckily, they aren't the only shifty characters on the train. But that small degree of good fortune quickly sours when powerful men turn up dead, suggesting the saboteur is still at work. And who better a mark for the murderer than the heirs to a foreign throne?