The house on the strand

Time-travelling back to fourteenth century England. A friend is lent a house in Cornwall and agrees to serve as "guinea-pig" for a drug his friend has discovered. The drug takes him back to the fourteenth century where he witnesses intrigue, murder and adultery. The more he time-travels the more he resents the time spent in his modern world. He wants to get back .....
A book you can't put down - you want to travel with main character to discover what happens.