At the time of Iron Council, several decades later, Spiral Jacobs still appears to be a good-natured bum slipping between varying degrees of coherency. He convinces Ori (truthfully or otherwise) that he was once a member of Jack Half-a-Prayer's gang, and helps him join Toro's revolutionary organization (later, Ori suspects he subtly furthered many of the revolutionary goals to bring the city into chaos). In the meantime, Spiral Jacobs lives up to his name by drawing spiral designs of varying complexity all over the city, even managing to get them as a symbol of the revolutionary movement.
When Qurabin the Teshi first sees a copy of one of these spirals on the traveling bag of a New Crobuzon refugee, he grows panicked, informing his traveling companions from the Iron Council that these spirals are part of a sinister and powerful Teshi ritual. The spiral designs covering the city - culminating as it turns out in an immense pattern in a corner of Perdido Street Station - are in fact a Teshi attempt to win their war with New Crobuzon by utterly eradicating it. Through supplication to the Moment of the Hidden and the Lost, Qurabin manages to prevent Spiral Jacobs from summoning the deadly urbanomach at the last instant. Spiral Jacobs, Qurabin, Ori, and Elsie are all killed in this final encounter.
While in Iron Council, the details and exact source of Spiral Jacobs' power seem mysterious until Qurabin reveals him to be Teshi, Miéville writes in Perdido Street Station that "By Tesh tradition, for example, the ambassador lived as a vagrant in New Crobuzon, communicating by mail for official business. Rudgutter would never meet him." This suggests that Jacobs was in fact serving as a Tesh agent throughout his time in New Crobuzon and that his kindness may be only affectation.
Once Ori and others become aware of Spiral Jacobs' sinister side, many of his incredible abilities are revealed. His designs peppering the city are impossible to remove, and he himself seems entirely immune to harm: attacks against him end with the aggressor mysteriously missing every time. When he finally lashes back at Ori, he sends him hurtling back with a gesture, melding his back into a brick wall. The little information Qurabin provides of this Teshi "ambassadormagik" labels Spiral Jacobs a hecatombist, master in turn of a whole series of thaumaturgies culminating in this final ritual. The power of this ritual is such that it sends "ripples" forward and backward in time in the form of temporary, dark and murderous manifestations or "haints" of psychic energy shaped like mundane people and objects.