<p>This research uses the lattice Boltzmann method to quantify&#xa0;the flow control mechanism around two duplicate inline square cylinders through a flat plate. The plate is placed in the second cylinder’s wake, and the gap (<i>g</i>) between the cylinder and the plate is precisely modified in the range from 0 to 10. The detachment gap (<i>G</i>) between both cylinders is set fixed at 3.5 which appear as the critical gap in case of inline bodies according to the published literature. The analysis mainly concentrates on figuring out the perfect parameters for the maximum fluid flow control across cylinders. A comprehensive examination of the fluid flow characteristics covering the vorticity evolution mechanism, streamline variations, drag and lift coefficient’s temporal behaviors,&#xa0;pressure fluctuations and Strouhal numbers depending on the varying <i>g</i> is conducted in the manuscript. Results indicate that, by progressively taking away the plate from the lateral cylinder, three&#xa0;separately distinct flow patterns appear: weaker vortex shedding in single-row pattern for <i>g</i> = 0 to 2, intermittent shedding flow pattern for <i>g</i> = 2.5 to 3.5 and strongly interactive vortex shedding pattern for <i>g</i> = 3 to 10. It is found that the splitter plate plays effective role in controlling flow at the close vicinity of the second cylinder and its impact gradually reduces as it is moved away. The <i>C</i>_Dmean reduces maximum up to 58.65%, <i>C</i>_Drms reduces maximum up to 48.05%, <i>C</i>_Lrms reduces maximum up to 59.76%, and St reduces maximum up to 5.96% as compared to two inline cylinders without plate case. Comparing the impact of plate on both cylinders, it is perceived that the plate controls the flow across the second cylinder more effectively as compared to the first one.</p>