Afterimage by Naomi Hughes

A horrific explosion levels part of the city and Camryn Kingfisher is the sole survivor.

Amidst controversy, conspiracy theories, and threats from government officials, Camryn longs for the truth. But the only person who she can turn to is a transparent boy in a lab coat named Quint. Unsure whether he’s a hallucination or a ghost, Camryn has no choice but to trust him as they become embroiled in a plot that is bigger than either of them realize.

In a race where the fabric of time and space is at stake, they must figure out who caused the explosion before the culprit comes back to finish Camryn―and her city―off for good.