A holy relic is cursed by its muslim keeper just before he is brutally murdered by Christian Crusaders in Jerusalem. The tale of the relic's journey covers many centuries and results in a series of deaths that have to be solved by a succession of sleuths. Each of the six authors portrays their own signature character and how their lives are touched by the relic & the intrigues surrounding it.
The collaboration results in a page-turning mystery with plenty of action and historical detail, in a varied but coherent style. It's also a good introduction to some of these authors if they're not currently known to you.