Fenner was the Principal Prison Officer, working on 'G wing' at HMP Larkhall Women's Prison, and was a regular major character during seven out of eight series of Bad Girls. The character was seen as a malevolent presence through much of the series, working the system and manipulating both prisoners and staff alike.
Throughout the seven series he appeared in, Jim Fenner made himself increasingly unpopular with prisoners and staff. He regularly abused the authority his position gave him and was seen committing several crimes including sexual assault, rape, GBH and even murder. In series three, he was stabbed with a broken bottle by Shell Dockley, who was seeking retribution for Fenner's past misdeeds against her.
During series four, Fenner finds himself the subject of (unwanted) sexual advances from Governor Grayling which lead to Grayling climbing into bed with Fenner.
After Fenner succeeds in having Neil sacked, he takes over as Acting Governing Governor of Larkhall, putting him in charge of the entire prison. True to form, Fenner abuses the power granted to him in his new position and uses it to further his own ends, rather than to assist with the rehabilitation of inmates.
There is also evidence to suggest that Tina O'Kane spiked a cheese straw during Neil's farewell party. However, none of these methods succeed in their purpose and Fenner manages to clamber to the doorway of the hanging cell, where he is met by Julie Johnston, who plunges an ice dagger into his neck. He died in front of the hanging cell where he murdered Yvonne.
He made two more appearances after his death in series seven. In episode 12 of series seven, he appeared as a ghost, walking the landings of G Wing in the final scene. In the Christmas Special he appears as a ghost, haunting Julie Johnston. It isn't clarified whether Fenner's appearance is the result of Julie not taking her prescribed medication for a bi-polar disorder.