Dark matter - Juli Zeh

Sebastian and Oskar have been friends since their days studying physics at university, when both were considered future Nobel Prize candidates. But after their graduation, their lives took very different paths; while Oskar holds a prestigious research post in Geneva, Sebastian worries that he hasn't lived up to his intellectual promise, having chosen marriage and fatherhood as an exit strategy.

A few days after a particularly heated argument between the two men, Sebastian leaves his son sleeping in the back seat while he goes into a service station. When he returns, the car has disappeared without trace. His phone rings and a voice informs him that in order to get his son back he must kill a man. As Sebastian's life unravels, the only person he can safely reach out to is Oskar...