"And Then I Found Out the Truth" by Jennifer Sturman

Delia's mom has been busy trying to save the environment down in Antarctica. But the big oil companies aren't fond of her attempts, and will stop at nothing to shut her up, including murder! Delia gets word that her mom is living underground in Argentina, where she's protected by a bodyguard, and safe...at least for the time being. Delia's been sent to New York City to live with her aunts, and is attending a very prestigious, private school. And there is a new boy around, Quinn, who turns out to be a romantic interest. Delia is ready to do some undercover work of her own to help her mom out, and put the criminals away. But things get complex, when she discovers Quinn's own step dad may be in on the plot to kill her mom. Going to Argentina seems like the only viable option to save her from danger...but will they be able to get there in time? This is the sequel to "And Then Everything Unraveled."