If the equation of plane passing through the mirror image of a point \( (2, 3, 1) \) with respect to line \( \dfrac{x + 1}{2} = \dfrac{y - 3}{1} = \dfrac{z - 2}{-1} \) and containing the line \( \dfrac{x - 2}{3} = \dfrac{1 - y}{2} = \dfrac{z + 1}{1} \) is \( \alpha x + \beta y + \gamma z = 24 \), then \( \alpha + \beta + \gamma \) is equal to: