As Holby City neurosurgeon Roxanna MacMillan lies in a critical condition following last week’s dramatic incident and Professor John Gaskell and Henrik Hanssen worry about her, flashbacks reveal how the trio became firm friends.

In America 1987, a young Hanssen (Harley Viveash), Gaskell (Michael Winder) and Roxanna (Isabella Marshall) meet at university and make a pact to push the boundaries of medicine, no matter what the cost. And it seems Roxanna has deeply personal reasons for wanting to make a difference…

Back in the present, brain surgeon Gaskell (Paul McGann) rushes Roxanna into theatre but Hanssen (Guy Henry) has reservations about him operating on their friend. As Gaskell urges Hanssen to trust him, another flashback reveals that, even as a student, Gaskell wasn’t entirely trustworthy…

Holby young Gaskell

A young Gaskell (Michael Winder) was fiercely ambitious, even as a student

“Viewers learn that Roxanna’s mother had a condition called locked-in syndrome,” reveals Hermione Gulliford, who plays modern-day Roxanna. “This is what made Roxanna want to study neurosurgery in the first place and it becomes very significant in the story.”

As the drama returns once again to the present, Roxanna’s life hangs in the balance. Gaskell, however, seems more concerned with how his stem cell trial could be under threat. How far will he go to preserve what he values most?

Holby City continues Tuesdays at 8pm on BBC1.