Fanciful plan (4,5)
I believe the answer is:
pipe dream
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fanciful plan</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for pipe dream that I've seen before include "Fantastic but vain hope" , "Unattainable hope" , "Sherlock's flight of fancy" , "Fantastic notion!" , ""Pie in the sky"" .)