Two-dimensional quantum field theory obtained by perturbing the q-state Potts-model CFT (0 < q < 4) with the energy-density operator PHI(2,1) is shown to be integrable. The particle content of this QFT is conjectured and the factorizable S matrix is proposed. The limit q --> 1 is related to the isotropic-percolation problem in 2D and so we make a few predictions about the size distributions of the percolating clusters in the scaling domain.