Ripper, by Stefan Petrucha

Orphan Carver Young has some general fantasies about becoming a detective, and devours novels and stories about  great sleuths, as well as serialized and sensationalized mysteries.  When ex-Pinkerton Detective Albert Hawking, cranky, contentious, eccentric, brilliant, and crippled, offers to take Carver on as an apprentice to share all he knows, Carver is ecstatic, even though it means living (for a reason I never really understood) in a private floor at the top of a mental institution, and getting more questions, half-hints, and criticism from Hawking than direct answers.  Carver's first and main "case" is to figure out the identity and possibly location of his father based on a scrap of a letter sent to the orphanage many years before.  As part of this Hawking introduces him to the "New Pinkertons", an underground (literally) and top-secret detective agency endowed by Alan Pinkerton upon his death. Hawking was head of the agency until his injuries forced him to give the reins to another former Pinkerton agent, Tudd, who is devoted to "gadgets" and buys many, many new mechanical, electrical inventions to help the secret agents with their investigations, and who is obsessed with catching a murderer, convinced it is the return of Jack the Ripper.

Tempest by Julie Cross

19-year-old Jackson Meyer can time travel.  Not much, usually just back a few hours or days.  And when he does go back, nothing he does actually impacts the future - no one remembers interacting with him if it happened on one of his jumps, if he hurts himself he isn't seriously damaged when he gets back, and if he does something on one of his jumps, like break a window, that thing is undone when he gets back to the present.  It's not really serving a purpose, but he's having fun experimenting, and keeping it a secret from everyone but his science genius friend who is helping him figure out why it's happening and how to use it.  At least it is all fun until some people who also appear to be able to "jump" back in time show up at his girlfriend's college dor, attempt to kidnap Jackson, and kill his girlfriend in the struggle.  Now Jackson has jumped back 2 years, farther than he's jumped before, and no matter how hard he tries, he can't get back to his "real" time.  And the Enemies of Time are still after him.

Star Crossed, by Elizabeth Bunce

Escaping from Green Men soldiers after a botched theft results in her partner's death, Digger convinces a boat of young nobles to help spirit her away, thinking they are helping "Celyn" escape from convent school.  Willing to leave the city of Gerse behind for awhile, Celyn becomes a maid to one of the nobles, a younger girl named Merista who is about to be presented to the marriage mart, and goes with Meri to reunite with her parents, exiled for the last several years for their part in a plot to overthrow the king and the corrupt church. 

The Agency: A Spy in the House, by Y.S. Lee, Bk 1

Only the Good Spy Young, by Ally Carter, Bk 4 in the Gallagher Girls series

In the previous three books in the series Cammie aka Chameleon Morgan has found out how serious being a Gallagher Girl is.  In the beginning it was fun knowing that she was a spy-in-training, sneaking out to meet a townie boy in Book 1 and using their special skills at detection, evasion, invention and deception to learn more about the mysterious boys from Blackthorne Academy in Book 2.