In this paper we consider the inverse problem of determining a rigid inclusion inside
a thin plate by applying a couple field at the boundary and by measuring the induced transversal
displacement and its normal derivative at the boundary of the plate. The plate is made by nonhomogeneous,
linearly elastic, and isotropic material. Under suitable a priori regularity assumptions
on the boundary of the inclusion, we prove a constructive stability estimate of log type. A key
mathematical tool is a recently proved optimal three-spheres inequality at the boundary for solutions
to the Kirchhoff--Love plate's equation.
