'Before your brain can register what you're being told, you know that something is wrong. And before you can respond, it's already too late. Because once you've heard those words, an event is set into motion and everything will change. "Help," he said. "He's not breathing."'

A tiny baby is rushed to hospital. Doctors find an injury to his brain and suspect he was shaken by his father, who is later charged and convicted. The baby grows up in the care of his mother. Life goes on.

Twelve years later, Ethan is now a singular young boy. Gifted with an innate affinity for physics and astronomy, Ethan sees the world in ways his classmates (and even his mum and teachers) simply can't - through a prism of light, time, stars and space.

Ethan is the centre of his mother's universe. Claire has tried to keep him safe - from illness, from feeling 'different', and from finding out what happened when he was a baby. But the older Ethan gets, the more questions he asks about his childhood and the father whose lifelong absence can't be explained by a single crushed photograph and a name, Mark, which is all Ethan has of him to cling to.

A single handwritten letter is all it takes to set off a chain of events which demand the gravity of pure love pull both parents into Ethan's orbit. As the years seem to warp and bend, the past is both relived and revealed anew for each of them.

Relativity is an irresistible story about love, unbreakable bonds, irreversible acts and science.