Zack was living a normal life until he met the Doctor, who had recently regenerated. When they defeated an Axon, Zack joined the Doctor in the tardis and travelled in Time and Space. When they arrived in the 1950s they encountered a deadly Virus which was sent from the 22nd century by Crastoff to kill the humans (this is unaware to the Doctor until later on). In one of there adventures the Doctor gets taken for experiments by the Srunks. Zack had to flee to the tardis during this time, so that he could work out a way to save the Doctor. Eventually he saves him and the Doctor finally tells him about the Timewar.