Dr. Grace Monroe is a scientist, mechanic and the wife of Henry Deacon in the alternate time line created after the Eureka Five time traveled to 1947.
Henry first met Grace briefly on Founder's Day 2010 before traveling into the past. When he returned to the (new) present day several things in Eureka had changed, and he found himself married to Dr. Monroe. Henry was distant towards his estranged wife and their marriage struggled. Eventually Henry started to develop feelings for his wife and told her the truth. Grace and Henry shared memories using a neural connection that Monroe invented.
In Season 5 it was revealed that the Henry indigenous to the new timeline had been working with Beverly Barlowe and Senator Wen, and that Grace had been persuaded by him to participate also.