She is the assistant of Giles Bretwithe. Famous in Midsomer Morchard for her bitter, acid and nosy behaviour for which nobody likes her. Everyone, jokingly or not, wonders how Giles can stand her.
She's in love with her employer, but he could never reciprocate her feelings, being homosexual. However, even though his sexual orientation was not a secret, she kept refusing to accept it and, when she accidentaly saw him making out with Sebastian Farquaharson, she convinced herself that Giles had been manipulated. Then she started preventing the two to meet again, justifying herself by saying that this was for Giles' own good, and started blackmailing Sebastian, again managing to convince herself that what she was doing wasn't blackmail because it was Sebastian who offered her the money to not tell anyone his sexual orientation.
When Giles is killed, Iris suspects that the killer is Sebastian and confronts him about, but the latter accuses her instead.
After discovering that Giles and Frank Bishop have manipulated Gerald Farquaharson to make him loose his mansion on a bet, Iris blackmailed him too using the document that legalizes the bet and that she has hidden inside the bronze statue in the middle of Midsomer Morchard's town square.
When DCI Barnaby discovers her action against Sebastian, she keeps claiming that what she did was not blackmail. The policeman obviously doesn't believed her, but doesn't arrest her yet because he understood that she's probably blackmailing someone else, and that this someone might be Giles' and Frank's killer.
Left alone, Iris comes home, but finds it all in disorder. She then calls Tom Barnaby, asking him to wait for her in Midsomer Morchard's town square, probably wanting to tell him the truth and to give him the document, but in that moment Gerald arrives and kills her by suffocation. Tom Barnaby and DS Ben Jones wait for her, but when she doesn't arrive, they go to her house where they found her corpse.
Going back to the town square, Tom finds the document, thanks to which he's able to discover Iris' killer and to arrest him. According to Gerald, her blackmail wasn't made for money, but for revenge. For this, when he's arrested, he acknowledges that Iris, like himself and the other victims too, was quite worthless so not a big loss for society.