As clued by the flavor text, each of these books is part of a series. We start by finding the name of that series (without any leading a/an/the) and the number of that book:
| Boy-Crazy Stacey | Baby-Sitters Club | 8* |
| Long Haul | Diary of a Wimpy Kid | 9 |
| Stay Out of the Basement | Goosebumps | 2 |
| On the Banks of Plum Creek | Little House on the Prairie | 4 |
| Surprise Island | Boxcar Children | 2 |
| New Moon | Twilight | 2 |
| Tyrannical Retaliation of the Turbo Toilet 2000 | Captain Underpants | 11 |
| Prisoner of Azkaban | Harry Potter | 3 |
| Amber Spyglass | His Dark Materials | 3 |
| Bad Beginning | Series of Unfortunate Events | 1 |
| Midnight on the Moon | Magic Treehouse | 8 |
| Titan’s Curse | Percy Jackson and the Olympians | 3 |
| Insurgent | Divergent | 2 |
| Yucky Blucky Fruitcake | Junie B. Jones | 5 |
| Brightest Night | Wings of Fire | 5 |
If we use the numbers to index into the names of the series, the clue phrase Two Towers Series is revealed. The Two Towers is the second book of The LORD OF THE RINGS.
Testsolving revealed that the graphic novels of The Baby-Sitters Club skip Claudia and Mean Janine, leaving Boy-Crazy Stacey as the seventh book. Fortunately, both the seventh and eighth letters give a T.