We report significant details of the magnetic structure and spin dynamics of obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation of the spins away from the principal axis, and they determine that the rotation is toward the axis. In addition, we find a significant spin-canting component along . The possible causes of these components are discussed, and their significance for the magnetoelectric effect is analyzed. Inelastic neutron scattering along the three principal directions reveals a highly anisotropic hard plane consistent with earlier susceptibility measurements. Using a spin Hamiltonian, we show that the spin dimensionality is intermediate between - and Ising-like, with an easy axis and a hard axis. It is shown that both next-nearest neighbor exchange couplings in the plane are in competition with the strongest nearest neighbor coupling.