|The Lost Hero|
|Series 05, Episode 13|
|Airdate||21 March 2011|
|Previous||Day of the Jacket|
|Next||The Fall of SKUL|
The Lost Hero is episode 13 of Series 5.
While trying to stop SKUL stealing a valuable data disc, Oscar Cole behaves recklessly and is ordered to stand down by the Head of M.I.9. Back at HQ, he confronts the Head of M.I.9 who tells him to stay off duty until he has calmed down. Angry and frustrated, Oscar decides to infiltrate SKUL and bring them down from the inside, on his own. He tells Rose Gupta and Carrie Stewart to keep quiet about his plan and they reluctantly agree.
When M.I.9 trace the SKUL agents to a warehouse, Oscar gets there first and persuades their leader Vincent to let him join them. With M.I.9 approaching, Oscar and Vincent escape. In the process, Oscar drops the signet ring his father, former M.I.9 super spy Edward Dixon Halliday; gave him before he disappeared 11 years ago. When Rose and Carrie arrive, they spot the ring and realise that Oscar has found SKUL.
When the Grand Master sees Oscar he tells him to prove his loyalty to SKUL by helping them to kidnap the Head of M.I.9. Meanwhile, Rose and Carrie realise that Oscar is in danger and decide to visit his foster family in the hope of discovering more about his plan. They are shocked to discover that he lives with an M.I.9 agent, not a family, and more surprised still when they find out that Oscar has been desperately trying to find out what happened to his father. All the evidence suggests that he is dead, but Rose and Carrie spot a lead that Oscar's missed and set out in search of Edward.
- This episode marks the last appearance of Rose Gupta, Carrie Stewart, Oscar Cole, Avril Franklin, Davina Berry, Donovan Butler, and Scoop Doggy.
- This episode marks the last appearance of Hermione King until Series 7 episode, "The Mayze", where she returns as a series regular.
- Jade Dixon-Halliday is mentioned.