The 1-nm-wide Bi nanoline has been proposed as a possible template for the growth of very-high-density arrays of atomic-scale nanowires, grown epitaxially on the technologically important Si(001) surface. Indium reacts with the Bi dimers, forming a unique zigzag atomic chain structure. Simulations of the appearance in STM of the lowest-energy isomer of this structure match experimental filled-states images. Calculation of the LDOS for the single-layer islands, finds that the nanowires are semiconducting, with a band gap smaller than that of the substrate, in good agreement with STS. A delocalised LUMO state is created, which may provide a conduction pathway along the nanowire. We have performed dual-probe STM conduction measurements along the In-Bi nanowires to test this prediction.