Rani discovers that one of her classmates has found an alien pendant which allows the wearer to control the minds of others. But the power comes at a terrible cost, and she is able to retrieve the artefact and bring it to Sarah Jane's attic for safekeeping. However, Sarah Jane is out of town, and Luke is staying with the Langers. Without warning, Clyde's long-absent father, Paul, shows up and expects to reconnect with his son. Clyde is reluctant, but he inadvertently gives his dad the opportunity to steal the pendant. Paul quickly finds the lure of its power irresistible -- and one of his first acts is to make Clyde forget all about his friends.

Joseph Lidster began his professional writing career with Big Finish Productions, the company which owned the licence to produce original audio dramas featuring the cast and characters from twentieth-century Doctor Who. His first play was a Seventh Doctor adventure called The Rapture, released in 2002, and he thereafter became a prolific contributor to Big Finish's various audio ranges, while also writing short stories for their Doctor Who prose line. In 2005, Lidster began developing Doctor Who material for the BBC's online presence. This led to Lidster receiving a commission to write A Day In The Death for the 2008 season of the adult-oriented Doctor Who spin-off Torchwood.

Late in the development of the second season of The Sarah Jane Adventures, Lidster was approached about contributing a script for that series as well. Executive producer Russell T Davies wanted it to focus on Clyde Langer; he suggested that it should introduce Clyde's estranged father, and take the form of a “road trip”-style adventure. Lidster was instructed to keep Sarah Jane's involvement to a minimum, as his story would afford star Elisabeth Sladen some downtime in the middle of the production schedule, much like Whatever Happened To Sarah Jane? had accomplished the year before. Since Lidster's scripts would be filmed as part of the season's second production block, they would be made alongside the season premiere, The Last Sontaran, which was designed to write Maria Jackson and her father, Alan, out of The Sarah Jane Adventures. As such, Lidster was also asked to include a small role for Maria and Alan as a surprise for viewers.

Traditionally, the Berserker was a Norse warrior whose power was enhanced by mindless rage

Lidster developed an idea around the tradition of the Berserker, a type of Norse warrior whose power was enhanced by entering a state of mindless rage. The serial ultimately bore the title The Mark Of The Berserker. Seen for the first time as Clyde's mother, Carla, was Jocelyn Jee Esien, who had written and performed in her own comedy sketch show, Little Miss Jocelyn, while also starring in the hidden camera comedy 3 Non-Blondes. Esien's dramatic appearances included episodes of The Bill and Holby City.

The first day of recording for The Mark Of The Berserker, under director Joss Agnew, was May 21st, 2008. Work at the show's regular Upper Boat studio facilities involved the sets for the Chandra residence and Sarah Jane's attic. Bannerman Road sequences were then filmed at Clinton Road in Penarth on the 22nd. May 26th and 27th concentrated on scenes at Park Vale Comprehensive, doubled as usual by Cardiff High School. Part of the 27th was also spent on scenes of Carla in her automobile, which were taped in Cardiff along the A48 motorway and at the intersection of Lakeside Drive and Torrens Drive. On May 28th, a house on Henllys Road in Cardiff posed as the Langer residence.

During the first two days of the following week, June 2nd and 3rd, Agnew concentrated on Clyde and Paul's “road trip”, with filming at Dunleavy Drive in Penarth and on the A4232 in Cardiff on the first day, and on Queen Street and at the Amante 9 Super Car Club in Cardiff on the second day. Work on June 4th and 5th concentrated on the climactic scenes at the Lynport Marina, which was actually the Cardiff Bay Yacht Club. The 6th was largely spent in Cardiff at Victoria Park, although the closing attic sequence was also taped that day at Upper Boat. It was back to Clinton Road on June 8th and aditional material was filmed there on the 9th, although Agnew's main focus was further recording on Henllys Road. Inserts were captured at Upper Boat on June 10th and 13th, as were more scenes in the attic on the 13th and 27th.

Unfortunately, Maria actress Yasmin Paige had fallen ill during her limited availability, resulting in some juggling of Agnew's plans and the arrangement of additional recording after Block Two had ostensibly wrapped. The chief make-up day was July 18th, which began with Sarah Jane's mission to find Travast Polong, taped at Llandough Hospital in Cardiff. Maria and Alan's surprise appearance was then filmed, with a house on Bettws-y-Coed Road in Cardiff posing as the Jacksons' apartment in Washington, DC. This left only some pick-up shots to be completed at Upper Boat, on July 23rd and August 1st.

• Doctor Who Magazine Special Edition #23, 24th December 2009, “Episodes 2.7/2.8: The Mark Of The Berserker” by Andrew Pixley, Panini Publishing Ltd.