Dr Who and his grandaughters Susan and Barbara show their new friend Ian their invention, TARDIS, a time machine. Unfortunately TARDIS takes them to the planet Skaro, home to the peaceful Thals and the deadly Daleks.
While attempting to cure the sickness caused by the radiation on Skaro, they soon join forces with the Thals teaching them to fight against the evil Daleks.
This was the first time ever that a Doctor Who story had appeared in colour.