The gathering of the Irises in the Death Zone

An adventure involving the gathering of several incarnations of Iris Wildthyme in the Death Zone by Morbius was never seen yet often referred and alluded to by Iris Wildthyme. The Eighth Doctor considered it to be a "farrago of lies and deceit [...] and outright stealing".

Either five, (PROSE: From Wildthyme with Love) seven, (PROSE: The Blue Angel) eight, (PROSE: Bafflement and Devotion) or every incarnation were gathered. (PROSE: Verdigris)

Arrival
After Morbius fell into the chasm at the hands of the Fourth Doctor, (TV: The Brain Morbius) the Doctor never suspected that the Sisterhood, lead by newly-appointed High Priestess Ohica, had rescued the injured Morbius. They brought him to the Death Zone, and after Ohica learnt that the "Beryl Reid" Iris had inveigled herself within the Sisterhood, she had used the Time Scoop to gather Iris' seven incarnations, (PROSE: Verdigris) though the "Jane Fonda" Iris recalled that it had been Morbius who activated the Time Scoop to reinitiate the Game of Rassilon. (PROSE: The Scarlet Empress)

Paul Magrs wrote in a prose piece that it had been the "Edith Sitwell" Iris who had called upon seven other Irises. This was also cited by Iris Wildthyme's Seven of Thirteen. (PROSE: Bafflement and Devotion)

Defeating Morbius
The Irises fought the Ice Warriors, the Ogrons, the Sea Devils, the Zarbi, the Mechanoids, Quarks, (PROSE: The Scarlet Empress) and the Voord. (PROSE: Verdigris)

The "Jane Fonda" Iris later recalled that she and the Iris covered in numerous coats and cardigans had looked at each other with "wary disdain" at the climax of the adventure in the "freezing mausoleum", (PROSE: The Blue Angel) the Tower of Rassilon, (PROSE: The Scarlet Empress) whilst the other five looked on, appalled. (PROSE: The Blue Angel)

Legacy
In Iris' bus, the Eighth Doctor read Iris Wildthyme's diaries, and had a go at Iris for her theft of his adventures, and that if the information got into the wrong hands. Iris, of course, defended the diaries and stood firm that she had also experienced these adventures which could coexist with the Doctor's. (PROSE: The Scarlet Empress)

Other accounts
According to Panda, he met five incarnations of Iris Wildthyme who had been "pooper-scoopered" by "some absolutely awful foe from the future", albeit not including the incarnation he usually travelled with. The five Irises fought the Voobi, the Gaar, the Bummies, and the Chumbloids. The "earliest incarnation" had cackled about how only the "rubbish" monsters were only present.

Later, Panda and the five Irises found themselves in a place very similar to the ballroom in the Blackpool Tower. There, they confronted the villain, who turned out to be PAND-R. Panda wrote about this in a letter to his Iris, who was disturbed she was left out, and suggested that she should be edited in through old footage, as she "hate[d] to be left out". She alos dubbed the adventure "The Five Irises". Panda then went off with the "Jane Fonda" Iris. (PROSE: From Wildthyme with Love)

Behind the scenes
This oft-alluded to adventure is somewhat of a "Noodle Incident" - a "Noodle Incident" being a fan-term for an event that is referenced by characters that is never shown, with little context or detail given about said event for comedic value. In this case, there is a bit of detail about the event, with the comedy stemming instead from how each story that references it giving slightly contradictory information.

Information from invalid sources
However, one account showed the "Beryl Reid" Iris, Thomas Daley, and Alistair investigating the disappearance of Ministry equipment, to find "Mr. O" claiming that he had stolen the equipment, holding it for ransom. They met the "Jane Fonda" Iris, who was then touched by an anti-matter creature, transporting itself and the "Jane Fonda" Iris to the Death Zone. Iris was later contacted by her "Edith Sitwell" incarnation, who asked her where the "Jane Fonda" Iris went - the "Beryl Reid" Iris assumed the universe of anti-matter, but the "Edith Sitwell" Iris corrected her and told her that the "Jane Fonda" Iris, alonb with the the other Irises, had beeb kidnapped and taken to the Death Zone, which the "Beryl Reid" Iris tried to claim didnt exist. (NC: Entertaining Mr. O)

Also, when the Third Doctor and Jo met Ian and Barbara in Devil's End, Jo, whilst on the phone to Mike Yates, saw a double-decker bus materialise outside in the heavy snow, bound for the Death Zone. (NC: Cheese and Crackers)