The Jezebel Tripp book 'Chromosome Wars' featured in Sins Of Commision, appears again in the second show of Season 9.
Susan Engel plays Camilla Crofton in this episode. She returns in episode 14.1, Death in the Slow Lane (2011), in the role of Harriet Wingate.
Mark Umbers plays Neville Williams in this episode. He returns in episode ?, Blood Wedding (2008), in the role of Harry Fitzroy.
Victoria Wicks plays Helen Callaghan in this episode. She returns in episode 11.7, Talking to the Dead (2008), in the role of Sarah Stone.
Several Doctor Who Alum here. Barry Jackson (Dr. George Bullard) and Susan Engel (Camilla Crofton) from the Tom Baker era. Robert Whitelock (John Denton) of the Matt Smith era. Donald Sumpter (Tim Settingfield) from the Peter Capaldi era.