Molly of Mars and her Alien Sister. Molly of Mars, #3

Molly and Pirra have always gotten along famously. They share the same bedroom, they tell each other every secret, and they're best friends. Quickly though, Molly finds out that growing up has a way of changing every relationship in her life, even the one she cherishes the most. Pirra's new responsibilities make her unbearable. Molly tries to repair the damage when she gets invited along with Vicky and Pirra to a party for ultra popular Heidi Hollisters.
But it doesn't work our how Molly expects. Separated because of a blow up, Molly finds herself regretting everything she'd did that night. Her relationship with her sister will never be the same. She and Vicky set out to solve the mystery of what happened. In the process, she uncovers more about the Alien Syndicate and faces off against masked men, aliens, and her own regrets. For ages 10+, Harry Potter level reading.