The Devil's Arithmetic

The Devil's Arithmetic, by Jane Yolen, is an historical fiction novel about the Holocaust, geared toward younger readers.  Thirteen-year-old Hannah is on her way to celebrate Passover with her family, but she'd much rather stay with her friend Rosemary, eating Easter candy.  She feels like every year, the Seder is the same - they do the Seder ritual with dinner and the adults talk about the past, and how important it is to remember.  Hannah doesn't want to talk about things that happened so long ago, and she gets bored of her family's stories.  

When her Grandpa Will declares that she will be the one to open the front door for the prophet Elijah this year, Hannah feels silly, but she goes along with the tradition.  Upon opening the door, however, she doesn't see the apartment building's hallway and the doors to the neighbors' apartments - instead, she finds herself transported to another time and place.  She has, in fact, been transported to Poland of the 1940s, where she will come to experience for herself the horror of the stories she used to dismiss.

Ticker

In Ticker, by Lisa Mantchev, we follow Penelope Farthing (who rides a motorized velocipede, lol), her twin brother, and their friends on a romp of suspense and intrigue as they try to track down the Farthings' kidnapped parents and the now-madman who was once the family's trusted friend and physician.  

Penny was born with the same defect of the heart which claimed the lives of both her sisters; after a traumatic accident, Warwick surgically removed Penny's biological heart and implanted what was only meant to be a prototype of its eventual clockwork replacement.  However, when the truth comes out about how Warwick developed and tested the clockwork "Ticker" on people he abducted off the street, the family is shocked, and Penny becomes unkindly known as the first of the "augmented" - an abomination in the eyes of some.  But Warwick's trial is underway; maybe once he has been convicted, the family can begin to move on and try to find some peace.

The day of the verdict goes anything but smooth, however - there's an explosion at the Farthing family's factory, where Penny was on her way to meet her brother.  On top of this, their parents have been abducted, and the ransom demands not money, but the family's Augmentation research.  With what seems a little twist at every turn, will Penny and her friends be able to find her parents before any harm comes to them?  Will she even be able to solve this before her worn-out prototype Ticker finally gives out?