Turbine inlet temperatures are continuing to increase as driven by the need to improve the engine's performance. Moreover, thermal pattern factors exiting the combustor are being driven towards a flatter profile to reduce NOx combustion, which in turn gives high temperature gradients near the vane endwalls. For these reasons, the endwall of the first vane is subjected to severe heat transfer conditions. To combat these high heat transfer levels, film cooling is generally used and is proven to be one of the most effective cooling methods for the endwall. This paper presents a computational study of a film-cooled endwall that also includes a realistic upstream slot, representing the combustor-turbine junction, and a midpassage gap, representing the mating between adjacent vanes. The focus of the results is on comparing adiabatic film-cooling effectiveness levels on the endwall with varying upstream slot widths and varying geometries of the mid-passage gap. Changes in the upstream slot widths occur because of thermal expansions and contractions during engine operation. Varying the inclination angle of the midpassage gap produced varying results along the endwall. The predictions indicated more effective cooling on the endwall as the gap flow was injected towards the suction side of the vane relative to the gap flow being injected towards the pressure side of the vane. The area showing the most improvement in cooling for injection towards the suction side was the trailing edge region along the suction side of the airfoil.