Kelsey Hooper

"I'm so shamed!"

- Kelsey Harper

Kelsey Harper was the first schoolmate Maria Jackson met after moving to Bannerman Road.

Kelsey was an apparent neighbor of Maria, as she approached Jackson because she noticed the moving vans. Almost immediately after meeting Maria, she suggested they go into town on the free Bubble Shock! bus. The ride was only free, however, because it made a mandatory stop at the Bubble Shock factory. She and Maria got embroiled in the mysterious happenings at the factory, and soon met The Archetype, who would later come to be known as Luke Smith. She herself was briefly held prisoner by Mrs. Wormwood and used for her knowledge of Sarah Jane Smith.

Although she would thrust her way into Sarah Jane's attic, and met K-9, she was not involved with the final remedy to the Bane crisis, because she was under the influence of the Bane chemical.

After having been released from the influence of the Bane, she was later described by Maria as "backtracking like mad — saying there's no such thing as aliens". In light of this, it was perhaps unsurprising that she was never seen again around 13 Bannerman Road.

Behind the scenes
Although the finished production of Invasion of the Bane easily allows for the character's absence in later episodes of The Sarah Jane Adventures, it's unclear whether actor Porsha Lawrence-Mavour was originally meant to have been a series regular. According to two reputable — but nonetheless unofficial — sources, the actor was not particularly easy to deal with on set, and may have been blocked from returning. No one from BBC Wales has ever publicly addressed the issue.

Of course, it is also possible that the SJA production team decided that having 3/4 of the main cast female would make the show un appealing to the male audience.