Robert Silverberg 
Up the Line 

Time travel spelled problems for the couriers of the Time Service. Shuttling backwards and forwards over the centuries they had to be wary of creating paradoxes – like meeting themselves watching the sack of Rome, or sleeping with their own ancestors.Of course, it also gave them the chance to amass wealth by the discreet use of their prior knowledge. The penalties were fierce and the Time Police implacable in their pursuit of lawbreakers. But it was still worth taking the risk.Jud Elliot took it when he met the marvellous transemporal paradox called the Pulcheria. He couldn’t resist her charms – the effects spanned generations, and set the Time Police on his trail!