Image Credit: Adrian Rogers, BBC Worldwide (this image appears for illustrative purposes only and no attempt is made to supersede any copyright attributed to it)
Major Alec Palmer was a ghost-hunter with many degrees.
He was, according to the Eleventh Doctor, a "member of the Baker Street Irregulars who specialised in espionage, sabotage and reconnaissance behind enemy lines," as well as "a talented water colourist and a professor of psychology." He kept some of his true occupations secret.
He killed in the war and sent many people to their deaths. Amongst the operations he was involved in was at least one that disrupted U-boats in the North Sea and Operation Gibbon. When he made it back from the war, he became haunted by this and became a ghost hunter. By 1974, he had bought Caliburn House and had his empathic psychic assistant, Emma Grayling, find out about the Caliburn Ghast while he took pictures.
On the fourth day of ghost hunting, 25 November 1974, the Eleventh Doctor arrived with Clara Oswald to ask Emma what sort of girl Clara was. Under the guise of a member of the ministry, he pretended to join in with the ghost hunting. With Alec's help, the Doctor discovered the ghost was the time traveller, Hila Tacorien, trapped in a pocket universe. With the help of Emma's psychic powers creating a wormhole, Hila was pulled out of the collapsing pocket universe, but she was unable to keep the connection and the Doctor was left behind. Alec convinced Emma to reopen the wormhole, and Clara rescued the Doctor in the TARDIS.
The Doctor told Alec and Emma that Emma's psychic connection to Hila was so strong because Hila was their descendant, and what Alec and Emma needed to was to "hold hands" and to "keep doing that, and never let go".