Episodes Broadcast: 2006-2008, 2015

A native of Wales, Catherine Tregenna got her start in television as an actress, opting to use her maiden name for professional purposes rather than her married surname, Morris. During the Nineties she appeared in Welsh-language programmes such as Pobol y Cwm, but she started to find acting roles scarcer as she matured. As such, around the turn of the century, Tregenna took up writing, and she found initial success with the play Art And Guff. Next came television scripts for Belonging, Casualty and her own co-creation, The Bench, before Doctor Who executive producer Russell T Davies recruited her for the first season of the spin-off series Torchwood. Tregenna would ultimately write four scripts for the show, starting with 2006's Out Of Time.

Tregenna thereafter contributed six episodes of Law & Order: UK, while also writing for programmes like Lewis and DCI Banks. When former Torchwood script editor Brian Minchin became the executive producer of Doctor Who, he encouraged Davies' successor, Steven Moffat, to solicit a script from Tregenna. She declined the invitation, however, advising that she didn't view herself as a good fit for the show. Nonetheless, Moffat and Minchin decided to wait until they had a project which suited Tregenna's talent for exposing the emotional core of her characters. She was finally persuaded to write 2015's The Woman Who Lived, in which Peter Capaldi's Twelfth Doctor was forced to confront the ramifications of the immortality he had bestowed upon Ashildr (Maisie Williams) in the previous episode, The Girl Who Died.

Tregenna went on to write for Lucky Man. Amongst her credits during the Twenties were Riviera, The Watch and Three Pines.