Iain, played by Michael Stevenson, previously appeared on screen briefly last year as one of Sam Nicholls's army friends.
As Iain begins working with Jeff and Dixie, it's clear that he is extremely confident and may need to be kept in line. However, he soon gets a chance to prove his worth when the team are alerted to a terrifying bus crash.
In tense scenes, Iain manages to rescue guest character Anna just moments before there is an explosion on the wrecked vehicle.
Later, however, Iain finds himself in hot water with Jeff for not following instructions and endangering a patient…
Sam, meanwhile, is shocked to see Iain at Holby.
As they used to be an item, Sam can't help but wonder whether she's the reason for his arrival - especially since he seems to be jealous of Tom. Is Sam right to be concerned?
Casualty airs these scenes on Saturday (August 31) at 8.40pm on BBC One.
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