The story is too complex to fully summarise, but is essentially a look at how the world could be changed by a device that renders conventional(ie chemical reaction based)weapons useless. Worse than that, actually a liability. A scientist is working on the analogue of a laser for gravity – a ‘tractor beam’. His device doesn’t work, but instead detonates any explosive material within effect range instantly. And suddenly every gun, bomb and missile in the world is obsolete…..
The only drawback is that the story is extremely technical in nature, which perhaps limits the appeal for non-science minded readers (hence only 4 stars). But don’t let it put you off – stick with it. This is Clarke doing what he does best – taking a vision of a possible future and bringing it to us today.