Artefactum, by J.E. Tobal

Artefactum is a science fiction novel, written by J.E. Tobal; being fair, it is a book that feels really difficult to classify into a genre, because it shares characteristics with multiple genres, and the plot is far from the conventions. A story that starts as a simple tale about not being able to deal with grief ends up spawning several universes and timelines; and honestly, that complexity is probably one of my favourite things about this novel.

Sam, a bartender, one day discovers that his girlfriend Una owns an idol that allows travel to other realities. A match made in hell, until one day the tragic death of Una happens, and Sam starts his descent into madness, as he refuses to accept it, convincing himself that Una is still alive somewhere in the multiverse. He will slowly explore realities/universes based on Fear, Death, Dream, or even the Primordial Void, in the company of characters that are certainly special, such as Sal and Hazem.

But the story gets even weirder, when Sam discovers how it is possible to travel in Time; unraveling a plot which following it requires your full brain power. When timelines and universes start being weaved, the plot becomes complex but at the same time, really hooking, as I found myself glued to the pages once this second part started.
It is such a mindblowing experience, but probably the best way to get it is experiencing it by yourself (I'm actively trying to avoid spoilers in this review, because I feel they would make the experience significantly worse).

We could say that this is a slow-burn story, as the whole first part of the book is about building a foundation that allows creating of a complex story, and that sadly affects the pacing a bit, which lands on the slow side. The pay-off is huge, as the author plays with the notions previously introduced, and even twists the rules for the sake of creating tension.

Characters end up landing on a bit plain side, feeling sometimes underdeveloped in comparison with the rest of the world; most of them are introduced to play a role, more than to be a complete character, except for Sam(ael) and his son, who are the main characters in our story.

Said that, if you are looking for a speculative fiction novel that uses the concept of multiverses and timelines in a really smart way, Artefactum would be an excellent pick. Many interesting ideas used to weave a great story.