Hanssen, played by Guy Henry, finds himself in a dangerous situation when an unhinged man named Nick Mooney targets him in a twisted revenge attempt.
Nick (Sam Troughton) is the son of recently-deceased patient Ritchie, who died in the hospital's care in a previous episode.
The dramatic storyline begins when Hanssen receives a number of threatening phone calls at work, which leave him concerned over the safety of his staff members.
When he later learns that the mystery culprit is waiting for him in the hospital car park, Hanssen heads outside for a confrontation.
Discovering that Nick is behind the calls, Hanssen enters his work van in an attempt to talk to him - and quickly realises that he is furious over the way his father was a victim of the non-referral scheme.
Nick has his compensation money in the van with him and starts to burn the notes one by one, throwing them dangerously close to some nearby fuel cans.
He also has a nasty-looking spike gun in his possession, leaving Hanssen fearful when Nick suddenly handcuffs him to the table - trapping him in the van…
With Nick seemingly determined to get even whatever the cost, what will his anger mean for a rattled Hanssen?
Holby City airs these scenes on Tuesday, October 2 at 8pm on BBC One.
> Read the latest 'Holby City' spoilers and news
In the exclusive gallery below, Digital Spy takes an in-pictures look at the episode.
Photo gallery - Hanssen held captive in Holby City: