This paper presents an experimental and analytical study of a steel plate connection for joining walls in the Masonite Flexible Building (MFB) system. These connections are used partly for splicing the wall elements and partly for tying down uplifting forces and resisting horizontal shear forces in stabilizing shear walls. The steel plates are inserted in a perimeter slot in the plyboard panel (a composite laminated wood panel) and fixed mechanically with screw fasteners. The load-bearing capacity of the slotted-in steel plate connections are determined experimentally and derived analytically for different failure modes. The test results show ductile post-peak load-slip characteristics, indicating that a plastic design method for shear walls can be applied to calculate the horizontal load-bearing capacity. The slotted-in steel plate connection concept can also be used for joining shear walls to transverse walls for tying down purposes in order to simplify the stabilization system of the building. The use of transverse walls for resisting uplifting forces introduces a three-dimensional behaviour of the wall junction and a more effective load transfer.