Between Two Worlds is the second part of the planned "Timeshift Trilogy," following Timeshift. Here we meet again Paul Thorndyke, now 45 years old. As the director of Betalight Management Technologies he is now one of the most important men in society. Betalight, discovered decades earlier, is a means by which the people of the present (the year 2441 AD) can view events of the past. Betalight essentially acts as a recording tape that captures and holds events as they occurred.

A deadly killing ash covers the earth, and it was thought by some that by viewing events of the past, it could be discovered how the ash came into existence. Then, armed with that information, today's remnants of civilization could learn how it might be possible to eliminate it, to allow humanity to once again live in the open air. Now pockets of humanity exist only by living in domed enclosures or beneath the earth in tunnels and caves.

Betalight, originally thought to be only a unique viewing mechanism of the past, is now believed by some to be capable of allowing people to actually enter the past, to affect events of long ago. The title of this novel can be interpreted as meaning between the worlds of the past and the present. It can also refer to the tensions between the "surface" humans and those "Imperfs" who live in the caves beneath the earth, the caves now being exploited by the surface people. A fear of war between the two civilizations hangs over everything.

Tobias Raikhel, unbeknownst to Thorndyke, is performing his own private experiment to determine if it is possible to affect the past, and thus the future. At the same time, Thorndyke's best friend, Quentin Cottle, Senior Time Jumper, wants Thorndyke to authorize his own attempt to actually visit the past. If the past can be entered then perhaps the moment in time when the killing ash was first created can be discovered and, by a jumper entering time at that moment, be immediately eradicated before it can spread and cover the earth.

Between Two Worlds shows true dramatic flair in the action scenes. In one, a scene in which the past actually comes alive in the future, the reader can almost feel the lives (and beasts) of the past exploding into the present as they are snatched from the battlefield of America's Civil War and brought into the future, with unforeseen killing result).

A nice amusing scene occurs when one if the Civil War soldiers talks about wanting a "housewife" to fix his "bishops," speaking in the slang of the day. It takes a while for those in the future listening to him to understand what it is he is actually saying.

Unfortunately, the finale is somewhat anticlimactic. That might be due to the fact that this is the middle book of a trilogy, with the true windup yet to come. Still, it is a book published separately and so it has to stand on its own merits as a book. One is therefore justified in expecting a more dramatic finish than what is presented here. Between Two Worlds is an entertaining read that ultimately falls short in delivering on its implied rousing ending.

• Timeshift