1 color black from grayscale?

I have an image that gets scanned in as a sharp B&W image which in photoshop becomes a grayscale image. i need to convert it to just a 1-color black image. I'm not sure if i just don't remember how or just flat out don't know yet what procedure to do. would changing it to RGB mode and hiding 2 of the 3 colors in channels, then saving it, make it an official 1-color black? What is the best/correct way? I need it for high quality print job done in Indesign. Thanks.

If your image is already in Grayscale mode, then just place it in InDesign as such and it will print on the black plate only.

Thanks!! Thats what i needed to know!! :)