how did helen die in heartbeat

Helen Walker, a character in the TV series Heartbeat , died in an explosion at the Aidensfield police house. The explosion was caused by a homemade bomb planted by a disturbed schoolboy seeking revenge for the death of his dog during a police chase accident. This tragic event occurred at the end of the 15th series, on July 2, 2006, and left her husband, PC Rob Walker, devastated