The theme of “The Final Gambit” by Jennifer Lynn Barnes is family. The theme of “The Final Gambit” is nobody is left behind.

Towards the end of the book, Avery confronts Eve about the act she's putting on to get information: “You pushed us to ask Skye about the seal,” I said, staring Eve down. “You’ve been asking around about deep, dark Hawthorne family secrets. You pressed and pressed for answers on Toby."

Avery confronting Eve about her not being Toby’s daughter caused Grayson, Mallory, and Mrs. Laughlin all to not trust Avery as much as they used to. This is bad for Avery because she had worked for the past year to build her trust and bonds with everyone who lived and worked at Hawthorne House.

“What is wrong with you?” Grayson exploded as soon as we were outside. “Did you hear a word I said in there?” I asked, my heart breaking like cracking glass, bit by bit." “Clearly,” he said, his tone almost regal, “I was wrong about you.”  

If Grayson had let go of Emily after her passing, then he wouldn’t have fallen in love with Eve over her resemblance to Emily; he would’ve caught on to Avery’s suspicions. This quote proves that nobody is left behind.

Near the middle of the book, Xander hosts a karaoke party, but Grayson doesn't show.  “Where is Grayson?” Nash asked. And that was when I heard it- a sound halfway between a crash and the shattering of wood. Jameson jogged out to the hallway. There was another crash. “Music room,” he told us. 

Finding Grayson after he didn’t show up to karaoke caused Avery and the brothers to find the next part of Avery’s puzzle. This is good because it helped Avery so she could solve the entire puzzle faster and easier with the boy’s help versus by herself.

“The label,” I said. “If we try to tear it off, it might rip. But steam will loosen the adhesive…” Grayson held the steamer out to me. “You do the honors.” This quote proves that nobody is left behind because it shows that Grayson wanted Avery to be a part of solving the puzzle.

If the karaoke party had just continued without Grayson, then Grayson wouldn’t have been able to assist the group with the puzzles.

The theme of "The Final Gambit" by Jennifer Lynn Barnes is "Nobody is left behind".