Holding the Line: Longitude Zero Degrees by Dianne C. Stewart

With no time passing in the present, they would appear in broad daylight. Liv hoped the tourist crowd would be focused on the brass strip with the red LED printout that marked zero degrees longitude and so fail to notice the peculiar-looking foursome.

But there was no crowd.

The spacious brick-paved area in front of the Greenwich Observatory was planted
with grass. "Look, guys!" said Anthony. "It's gone!"

He was right. The dividing line between the Eastern and Western hemispheres, the Prime Meridian, was nowhere to be seen.

Liv read aloud the words on a brass plaque:

"After the assassination of George the Third, champion of John Harrison's H4 timepiece, which made possible the determination of longitude at sea, and the ensuing madness of Royal Astronomer Sir Nevil Maskelyne, England's prominence in that science was threatened. In 1884, the official Prime Meridian of the world was declared to be in Paris, France."

In Diane C. Stewart's latest time-travel fantasy, Longitude: Zero Degrees (Beanpole Books, 2009) Liv, Anthony, and Cal travel to London for a summer holiday where Liv's father is working. But on the airplane over the Atlantic, Anthony and Cal spot a familiar face, the former eighteenth-century pirate Robert Francis Morehouse, the man who tcaptured Cal and Anthony in 1772 and then saved the boys in exchange for his own safe escape to the twenty-first century. Now a semi-legitimate antiques merchant, Morehouse is travelling with two suspicious characters whom Liv immediately senses are tied up with Morehouse's past in a way which promises to be a danger to them as well.

Fearing that it might bring harm to any unsuspecting person who might find it, the three kids had decided to bring along the mysterious wooden box which has the power to move them through time. Then, trying to befriend Frederica, the troubled daughter of her mother's London friend, Liv accidentally spills the box from her backpack, and before she can stop her, Frederica opens it, taking them on an unexpected time trip back to 1772. There, in the garden of the Greenwich Observatory, they find themselves witnesses to a plot to thwart the astronomer John Harrison's plan to push his invention, a timepiece which will enable England's seaman to calculate longitude and thus rule the seas, a plot which results in the assassination of King George III right before the startled eyes of Liv and Frederica.

Knowing that this change in history will greatly alter England's future place in the world and endanger America's eventual independence, the four realize that they must return to 1772 to make sure that the proposed murder of George III does not occur, and to do so, they must enlist the aid of the only person who holds the key to the chain of events in 1772, the former pirate Robert Morehouse himself.

In this sequel to her 2008 fantasy Quimbaya (See my review here.) Stewart again shows that she can create believable and appealing young characters within a fast-paced historical chase which takes place simultaneously across four centuries.