Line Spacing when hitting the return key

I'm unable to adjust what happens when I press the return key. My document was working fine moving down one line upon pressing the return key but I pasted in some text which appears to have changed the formatting and now a return press moves down approximately 2 lines. I selected all the text making sure it was all the same size and font but no help. I seem to be able to hold shift and return to make what I think is a soft return but earlier I moved the same amount just pressing the return key. I've hunted through the formatting tools but clearly I'm missing something.

Thanks for your help.