Location: School of Fish
Depth: 247

Solution to Bookshelves

by John Hawksley

Answer: CROWDS

The clues clue 2-word phrases that can have a letter put inside to form a single word.

extra(C)table
news(R)eel
yell(O)wish
heavy(W)eight
screw(D)river
grave(S)tone

The answer is CROWDS. The title is another example of such a compound word.