Haines helped prepare the Z-Bomb for launch. It failed to launch, and the Cybermen took over the base. The First Doctor and the Cyberman leader, Regos Krang, agreed to negotiate, but Krang told them the talks could not begin while the rocket was aimed at Mondas. The Cybermen took Haines, Ben Jackson, Barclay and John Dyson to dismantle the warhead.
They began work, but when Doctor realised the Cybermen planned to detonate the bomb in the silo, he announced over the PA system the Cybermen's plan. They refused to continue to dismantle the warhead, and when Ben realised that radiation killed Cybermen, they planned to use the rods from the reactor to attack them.
Ben set Haines and Dyson up at the end of the corridor. When the Cybermen used gas to draw Ben and Barclay out of the silo, Haines and Dyson moved forwards with the rods. The Cybermen began to weaken, but one of the Cybermen managed to shoot and kill Haines. (TV: The Tenth Planet)