Jonas was a mysterious medium (played by Mark Heap) with the power to bring back the spirits of the dead to the world of the living. His attitude to his profession was similar to the recently deceased probation worker Shaun. He brought back Sally, Tony and Rachel after he acquired his power due to being caught in the storm.
After the Storm, Jonas had received the power of Communing, the ability to bring spirits of the dead to the world of the living. This was a reflection of his job as a medium (he was really a fake). He used his power to act as a type of communication between spirits and the living, also using it to bring spirits back to the world of the living, letting them deal with unfinished business, before then moving on. He managed to bring Sally, Tony and Rachel back to deal with their own business.