This essay studies gender in medieval heresy by focusing on an inquisitorial trial in Milan in 1300. The inquisitors investigated a small group of devotees of a deceased penitent woman named Guglielma for venerating her as the Holy Spirit. A noble Humiliati nun, who would become Guglielma’s pope in a coming new age, and a wealthy layman cooperated as the devotees’ leaders. On the surface, the devotees seemed to have reversed gender roles, which late medieval male clergy-female mystic partnerships exemplified. Through an analysis of the surviving records, this article demonstrates that, instead of inverting gender expectations as the inquisitors assumed, the devotees’ vision of a new age – somewhat infused with Joachimism – and the co-leadership of the nun and the layman developed out of transcending the gender binary. As a result, the devotees saw Guglielma not as a co-redeemer with Christ but as the Holy Spirit who comforted them, would convert non-Christians, and had helped unite the devotees, even those of opposing political factions, into a family. Rejecting violent rupture as well as binary gender roles, their future age, which would begin with the nonviolent replacement of the Roman Church, would both preserve Milan’s social hierarchy and eschew binary gender roles.