Septimus was a Cwej-Plus. He acted as Straxus' assistant on a mission to the 19th century. He was one of the Cwejen who went mad, warping trace memories of the Doctor into a "pale god" they called "Mister Seven". He conducted acts of murder involving the number seven that Bernice Summerfield and Mycroft Holmes were investigating, hoping that it will call the Doctor to him. He eventually turned on Straxus, forcing his regeneration. Benny and an earlier incarnation of Straxus defeated the mad Cwejen, which were taken back to the Homeworld for dissection. (AUDIO: The Adventure of the Diogenes Damsel)