Brian Aldiss 
Cryptozoic! 

In the year 2093, human consciousness has expanded to the point that man can visit the past using a technique called 'mind-travelling’. Artist Edward Bush returns from a lengthy 'trip’ to the Jurassic period to find the government overthrown by an authoritarian regime. Given his mind-travel experience, he is recruited by the new regime to track down and assassinate a scientist whose ideas threaten to topple the status quo. However, the job of an artist is not to take orders but to ask questions . . .