The Camelot Code: The One and Future Geek, by Mari Mancusi, for Timeslip Tuesday

Here's a fun timeslip story for kids that mixes computer gaming with the story of King Arthur and medieval magic--The Camelot Code: The One and Future Geek, by Mari Mancusi (Disney-Hyperion, November 2018).

The time has come for Arthur to pull the sword from the sword and become king!  But when Guinevere, his best friend, accidently drops a magical treasure down Merlin's enchanted well, and Arthur tries to get it back, he falls in himself....and travels through time to our present.  Merlin has set up the well to serve as a connection to the modern era, where he enjoys the benefits of Wifi, and plays an online fantasy game, Camelot's Honor, with two ordinary kids, Sophie and Stu. When Merlin realizes he's lost Arthur to the future, he calls Sophie and Stu back into the past.  With the help of Merlin's magic, Stu becomes a stand-in for Arthur, and Sophie goes back to the present to try to bring him back before the future is irrevocably changed.  And Guinevere travels down the well too, to try to do the same.

In our present, things become chaotic.  Already things from the original timeline are different.  Arthur of course is faced with tremendous culture shock, but finds that he quite likes high school--he makes friends with Lance (once Stu's stepbrother, but not in this new present), and joins the football team.  When he reads about himself via google, he is naturally horrified to learn what would have happened if he'd become king, and so when he meets Guinevere at high school, their relationship is strained (especially when Lance falls hard for her....).  More importantly, Arthur has no desire to go back to his rightful time.

Complicating things is the fact that Arthur's half sister, Morgana, has followed him to the future, where, being outside Merlin's protection, he'll be easier to kill!

Now it's up to Sophie to convince Arthur to come home (or else peperoni pizza will never be a thing, and she doesn't want to live in that world), while Stu struggles to hold the fort (literally and figuratively) while the threat of the Saxon invaders looms...

So there's a lot happening, but it all works together really well, and it's a lot of fun!  Merlin, dabbling with modern technology and trying to keep everything together, provides nice humor.  Geek girl Sophie is a delight, and Arthur's ultimate high school triumph is strangely believable.  There's some real-world emotional depth provided by the strain that's entered Sophie and Stu's friendship, when she's afraid he's drifting away from her preferred gamer-geek life, and she's afraid of loosing him (things move past geek gamers vs sports players, though- Sophie and Stu realize you can do both). And of course Arthur's struggle with his destiny, and his own relationship with Guinevere, is hard for him.

Recommended in particular to fans of Vivian Vande Velde's Heir Apparent series, which are also computer gaming mixed with fantasy.  Which is me.  I'll be looking for book 2, Geeks and the Holy Grail, when it comes out this October!

(Of course, the Arthurian past isn't a real "middle ages," but it still serves the story well).