The extremes - Christopher Priest

Teresa Simon has just become a widow, her husband shot in a seemingly unprovoked attack by a gunman on the loose. Teresa and Andy both worked for the FBI and used virtual reality programs to help them re-enact critical situations. Teresa goes to England to investigate another horrific mass killing which occured on the same day and in very similar circumstances. But she finds only the reflection of her own grief. Until, that is, Teresa joins GunHo - a virtual reality company. Relief comes in the worlds and personalities of other people's existence until she enters the mind of Gerry Grove, the town's assassin and is terrified by what she discovers - about herself.