2014 Focus Ecoboost 1.0 strange problem

Hi,

My 2014 Focus Ecoboost 1.0 has an unusual problem.

Arriving home, I removed the key but the engine kept running. Eventually, after turning the key several times did the engine stop. Then on returning to the car the same day, I found the battery (a new one) completely dead.

Has anyone come across this before and does anyone know the fix?

Thanks Malcolm