When an elderly priest passes away, one of his colleague discovers a mysterious green liquid hidden in a cylinder deep beneath a long-abandoned church. Rather misguidedly, as it turns out, he invites a group of enthusiastic students to come and investigate it's properties. Big mistake! It was hidden deep in the bowels of this crypt for a very good reason, and once they release it they discover that the Satanic horror they face might just be the tip of the iceberg! Donald Pleasence is strong here as the priest who realises, all too late in the day, that they are facing a terror that could jeopardise the very future of humanity... Christianity at any rate! Can he galvanise his now panic-stricken helpers to reverse the effects of the deadly gloop before they all become zombified servants of evil? The dialogue maybe isn't so hot, especially as hysteria begins to set in amongst the petrified, but the pace is great and the effects have held up remarkably well as this solid and quite menacing story builds to a genuinely exciting conclusion. The supporting cast deliver well, too and John Carpenter and Alan Howarth manage a score that adds quite a bit of peril to the accruing sense of danger the former creates throughout this rather superior drama. It's short, taut, and well worth a watch.