None : Robin Roughley's None Series Book 1

Ruben is a successful salesman.
Roz hates her boring admin job.
Ruben owns his own home.
Roz still lives with her nasty mum and dad.
One is a serial killer, the other desperate to learn the trade.
When high-school misfits Ruben Jones and Roz Smith's paths cross later in life, they see something in the other no one else has and they team up to form a friendship based on the one thing they have in common – murder.