"Help," he said. "He's not breathing."

A tiny baby is rushed to hospital. Doctors 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 a singular young boy. Gifted with an innate affinity for physics and astronomy, Ethan sees the world in ways others 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 protect him from finding out what happened when he was a baby. But the older Ethan gets, the more questions he asks about his absent father.

A single handwritten letter is all it takes to set off a dramatic chain of events, pulling both parents back together again 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 and irreversible acts.