Histories of the Great Fire of London regularly mention and reproduce Valentine Knight's scheme for London's reconstruction, published in 1666, and note that he was imprisoned for his pains. His proposal, with new streets laid out on a rough grid and a canal through the heart of the city, has attained a walk-on part in longue durée histories of urban planning. However, Knight has remained a mysterious and little studied figure; the significance of his imprisonment and of the fact that his was the only scheme to be published remain unexplored. By reconstructing his biography and discovering the reason for his incarceration, and by relating his and the other proposals for the rebuilding of the capital after the fire to the history of public opinion, this article uses this episode to explore the tacit rules governing the discussion of public affairs in Restoration England. Further, by examining the publication history of all the immediate post-fire schemes for rebuilding London from 1666 to 1750, it traces how architectural plans gradually became objects for critical discussion in the worlds of print and periodical.