The paper presents a set of one-degree-offreedom overconstrained linkages, which can be folded into a bundle and deployed into a polygon on a plane. The proposed mechanisms are movable Bricard octahedra of Type III, characterized by the existence of two configurations where all joints are coplanar. The possible geometries of doubly-collapsible Bricard linkages are parameterized and their kinematics is analyzed. A method is proposed to construct a bundle-compacting mechanism of this type, necessary and sufficient conditions are derived for the deployedconfiguration polygon to be a square. Case studies and simulations validate the analysis and design.