Describe Miles's plan. What was the drawback of the plan?

Mae Tuck has been arrested and put in jail for killing the man in the yellow suit.  She is likely to be hanged for her crime.  Miles's plan is to break Mae out of the jail.  He plans to do this by removing the jail cell's barred window.  He is going to take the window and frame out in one entire piece.  Then Mae should be able to climb through the window in order to make her escape.  

"He says he can take Ma's window frame right straight out of the wall, bars and all, and she can climb through."

The problem is that the constable is likely to notice fairly quickly that Mae is missing.  The Tuck family needs more time in order to put a lot of distance between them and Treegap.  

"But even if she can climb through the window, he'll come after her soon's he sees she's gone. Seems to me he'll notice right off. That don't give us much time to get away."

Winnie Foster solves that problem by volunteering to climb in through the window.  She will hide underneath a blanket on the bed, and the constable will think that Mae Tuck is still in the cell.  Winnie's actions would buy the Tucks a few more hours of escape time.  

"When your mother climbs out the window, I'll climb in and take her place. I can wrap myself up in her blanket, and when the constable looks in, he won't be able to tell the difference. Not in the dark. I can hump up and look a lot bigger. Miles can even put the window back. That would give you time to get away! You'd have at least till morning!"