McAllister was a captain in the Scottish army in 1759. He had "bristling black hair and dark little eyes that flicked this way and that". He arrested the Tenth Doctor for attacking Benjamin Franklin's coach and Martha Jones for wearing "pantaloons". He threatened to lock them up until the Lord Provost decided they should be hanged.
He ordered his soldiers to open fire on the walking dead, which angered the Doctor as they were showing no sign of attacking. His soldiers and he retreated, following the Doctor to Reverend Yarwood's church, where they waited. McAllister later accompanied the Doctor outside to confront the dead.