Finally--I feel like I've been reading nothing but disappointing books for months. Ubik is like a big-budget sci-fi blockbuster condensed to 200 pages: Full of action, intrigue, and a lot of confusing twists. I will try, without giving anything away, to explain the plot:
Sometime in the future, portions of mankind have developed psychological powers. These people are called psis, and come in various flavors, the two most important of which are telepaths and precogs. Precogs--you may recall from the Dick adaptation Minority Report--can predict the future. In the future, the psis represent a significant threat to business interests, as a rival organization may plant telepaths in your organization or use precogs to see what you're going to do, so "prudence organizations" use the talents of antis, who block psis' powers, to protect themselves. Glen Runciter is the head of one of these organizations, which he manages with help from his dead wife who is kept in "half-life"--a cryogenic stasis where communication with the dead can be maintained, although the more you speak with them, the closer they get to true death.
Runciter and his team, including his right-hand man Joe Chip, accept a job on the moon where they believe many of the world's greatest psis have gone to cause havoc. The job turns out to be a trap, and Runciter is killed--or so Chip and the others think. When the team returns to Earth to bury Runciter, they find that somehow every thing is reverting to its earlier incarnation--for example, automated pay elevators (you have to pay for everything in the future, even doors) have become old-fashioned elevators with steel grates and elevator operators. Cars are reverting to 1920's era-Model T's, etc., etc. At the same time, they seem to be receiving, on the backs of matchbooks and in newspapers, strange, cryptic messages from the dead Runciter, advising them to find a mysterious substance called Ubik, which is the only thing that can protect them when members of the team start dying off one-by-one. Luckily, it is available in convenient spray-can form. Whew.
I loved Ubik because it's unbelievably fun and quickly paced, as well as deeply funny. But it doesn't come off as hollow entertainment; Dick manages to weave some very interesting thoughts about God and death in as well. Ubik itself seems to be an analogue for God--after all, it comes from the Latin word ubique, meaning "everywhere." It is a protective force, preventing decay and staving off entropy, preserving the forward motion of time when all else is tumbling backward. A series of epigrams that begin each chapter tout Ubik as a commercial product (Can't make the frug contest, Helen; stomach's upset. I'll fix you Ubik! It takes more than a bag to seal in food flavor; it takes Ubik plastic wrap, etc., etc.), perhaps going so far as suggesting the commodification of God in this future society, perhaps suggesting that order can be found in the universe in strange places.
In any case, I highly recommend Ubik. Safe when taken as directed.