An inner Helmholtz layer model is proposed for the low-frequency dielectric dispersion of aqueous suspensions of submicron size colloidal particles. It is assumed that the ions in this layer are mobile but isolated from the outer layers (the outer Helmholtz layer and the diffuse layer). For relaxation frequencies of the inner Helmholtz layer much lower than those of the outer layers, the polarization of the inner Helmholtz layer is simulated using a random walk method. A Debye-type relaxation is obtained. Using parameters consistent with the range of experimental conditions, an excellent fit to data on suspensions of amphoteric latex particles is obtained, whereas the standard electrokinetic theory of diffuse double layers and the dynamic Stern layer model have both been unsuccessful in this regard. It is predicted that the polarization of the inner Helmholtz layer will become nonlinear and will saturate with applied fields at high field strength.