ward, Keller, while Sacha Levy (Bob Barrett) is a locum general surgery registrar. Joseph Byrne (Luke Roberts) and Greg Douglas (Edward MacLiam) are cardiothoracic registrars, and Oliver Valentine (James Anderson) is a F2 doctor working under Greg. Oliver's sister Penny (Emma Catherwood) is also an F2, and works on the Acute Assessment Unit (AAU), alongside sister Frieda Petrenko (Olga Fedori). Faye Byrne (Patsy Kensit) and Donna Jackson (Jaye Jacobs) are also ward sisters, on Darwin and Keller wards respectively, and Elizabeth Tait(La Charné Jolly) is a staff nurse on Keller. Mark Williams (Robert Powell) is the hospital's Chief Executive Officer. Guy Henry was cast as new joint Director of Surgery and consultant general surgeon Henrik Hanssen, who arrived in the series' first episode. His character is "a bit of a mystery man", apparently sent to the hospital by the Department of Health to make budget cuts. Henry describes him as "punctilious, pedantic and passionate about his work" with a dry sense of humour, and a rival to Connie. Tina Hobley returned as ward sister Chrissie Williams following four months maternity leave in November 2010, and used her infant son Orson to play Chrissie's son Daniel. Jimmy Akingbola joined the cast in January 2011 as general surgical registrar, Antoine Malick. Laila Rouass was cast as cardiothoracic surgical registrar Sahira Shah, appeared from February 2011. Announcing her casting, Daniel Kilkelly of media entertainment website Digital Spy described Sahira as a rival for Jac and love interest for Greg, who shares a "dark history" with Hanssen. Rouass was able to relate to the role as, like herself, Sahira is a mother attempting to balance her personal and professional lives. Campbell stated that Rouass brought a "fresh new energy" to the series and that Sahira had been a "joy to create", commenting on the character: "While on the surface she appears to be cool and calm, underneath it all, she is kicking madly just to keep afloat. It will be fascinating to explore what is really going on underneath the façade of perfection Sahira has created for herself. I'm sure her character will be someone a lot of viewers will recognise in themselves." Adam Astill was cast as consultant orthopaedic surgeon Dan Hamilton. Former Waterloo Road stars Sarah-Jane Potts and Lauren Drummond joined the cast on 7 June 2011. Potts plays senior staff nurse Eddie McKee and Drummond plays agency nurse Chantelle Lane. Recurring