After coming together through a music paper back-page ad, the twosome spent three years putting previous bad relationships behind them, then quietly moulding the Top 40-friendly yet heartfelt sounds that will probably be impossible to escape on the radio for the rest of the year.
"We weren't very pressured," Cassidy says, recalling their first year. "We threw away things if they were not up to standard. I had been in bands before, but my voice was always used more as an instrument. With Agnes, it is more featured."
And she puts it to great use on the forthcoming single, "Dumb", which, apart from being a sarcastic swipe at a particular know-it-all female in Cassidy's life, is also memorable for a bassline that's so hot it burns a hole through the whole song. Her voice swings from the sly, to the snarling, to the heatedly passionate and back again with a confidence that the band is also increasingly developing live.
So far they've clocked up a mere eight dates, mostly with The Warm Jets and Puressence, and had the misfortune to be reviewed for the first one at the Electric Ballroom a couple of months ago.
"We had no idea what she [the reviewer] was going to say," remembers Cassidy. "There were four bands and we were the first on, but we were able to pull it off. It was a bit overwhelming - it was a big stage, and people wouldn't come down to the front, so it was difficult to create an atmosphere. I didn't move from the centre - I felt glued to the stage. The next date with Puressence was much better; people were so close you could touch them."
For Agnes, the toil of gigland has only just begun. They will spend the best part of three weeks this month submerging themselves in smoky venues around Britain, but Cassidy wouldn't have it any other way. "It's been quite boring, waiting around," she sighs. "It's one of the worst parts of the industry, waiting for the next gig or record. I want to stay busy, carry on touring. I am not good at pacing the floor and staring at the walls."
Agnes play a free gig at the Felix & Firkin, 31 High Street, Barnet EN5, tonight