Lead Casualty writer Mark Catley will pen two episodes of the series, sandwiching a single instalment of its sister show for a storyline which sees a regular Casualty character being rushed for treatment on the wards of Holby City.
Speaking exclusively to Digital Spy, Casualty's series producer Oliver Kent said: "It's a very exciting one. I can't say too much at the moment, except to say that one of our most important characters will find themselves being treated in Holby City and another of our regulars will go along with them.
"The plan is that in the Casualty episode, which will transmit in February, the leading character concerned will be injured and their life will be saved by another leading regular. That injured regular will need to have their injuries treated in Holby City."
He continued: "Mark Catley, who's Casualty's lead writer will write the Holby City episode, too. We'll then pick up in the next episode of Casualty what happens in the aftermath."
The current crossover plans will be the fifth time the sibling shows have overlapped. The first, titled 'Love Nor Money' aired on September 16, 2003, before the second Casualty@Holby City Christmas special was televised in December 2004. Another double bill - 'Test Your Mental' and 'A Great Leap of Faith' - aired in October 2005, while the two-part crossover 'Deny Thy Father' broadcast at Christmas in the same year.
Kent added: "It's fantastic to be able to do the crossovers, but the difficulty is purely logistics. We film in Bristol and they film in Elstree. The will is certainly there!"
> Click here to read our full interview with Casualty's series producer Oliver Kent