This story is really tricky, plots within plots, and it seems that no one is who (or what) he seems to be. It might have helped if I'd read Stableford's novel, INHERIT THE EARTH prior to diving into ARCHITECTS.
The tale is something of a who-dunnit. It starts out with a most unlikely murder scenario set some centuries in our future. A pretty woman gives flowers to a man, and the innocent-looking blooms attack him in macabre fast-forward growth. The flowers kill him!
From back cover: Brian Stableford is back with a first-class hard SF adventure in the same future universe as INHERIT THE EARTH.
Five hundred years in the future, there is a murder in New York City by the agency of genetically altered flowers, and a rejuvenated plant designer named Oscar Wilde must help Charlotte Holmes of the NYPD investigate.
Stableford is very good at gradually unfurling his wheels-within-wheels plot, and he displays a commendable interest in exploring the consequences of biological advances.