Time travel juvenile fiction right in my wheelhouse!
Michael, a 12-year old living in 1999 and his 16-year old babysitter, Gibby, meet Ridge, a time-traveling teen from 200 years in the future. Their interactions, and how these interactions affect the multi-verse, make for a cool story.

I gave it 4 instead of 5 stars, because as an adult, I understood/enjoyed all the 1990s and 1999/Y2K impending doom references, but would it have the same nostalgic impact on a middle schooler today? I don't think so. ( )

It's 1999, and Michael and his babysitter Gibby - daughter of the man who fired Michael's mom, who now has to work three jobs instead of one - meet a strange kid called Ridge who reveals he's from the future. Michael is preoccupied with the impending Y2K, but Ridge won't tell him what's going to happen - yet the three of them all have an important part to play, and are woven together more closely than they might imagine.

Quotes/notes

STS = Spatial Teleportation Scientists
NTI = Native Timeprint Inhabitant

He wished there was a way to forget the things you knew. (Michael, 63)

"I wouldn't have traveled here if it was a dangerous time to be alive," Ridge said.
"It's always a dangerous time to be alive," Michael said. "Depending on who and where you are." (76)

"I know it doesn't seem glamorous or interesting to you right now," Ridge said. "But that's because no one realizes they're living history every minute of every day....Every breath we take, we're contributing to history." (94)

"It's not your job to figure out why walnut-brained people do walnut-brained things. It's your job to make sure you don't become one of those people." (Mr. Mosley, 101)

"The first state of being...the present moment. It's the first state of existence. It's right now...the past is the past. The future is the future. But this, right now? This is the first state, the most important one, the one in which everything matters." (Ridge, 118)

Conklin Principle: For every bad outcome you can anticipate, you should consider at least one positive outcome. (149)

He'd never experienced grief before. He didn't know the way it pulled at all your muscles and created an anchor in the center of your chest. (176)

"Sometimes history remembers people who don't deserve it and forgets the ones who do....Just because he isn't written down in a book doesn't mean he wasn't important." (Ridge to Michael, 191)

"Not knowing is part of life." (Ridge to Michael, 214)

"Everyone makes mistakes," Michael said quietly. "It doesn't mean you deserve only bad things." (215, and repeated, flipped, 222)

Not knowing might be part of life, but that didn't make it any easier. (223) ( )