A police dog was left seriously injured after being repeatedly stabbed while chasing an armed suspect.
Finn the dog and his handler had been in Stevenage responding to calls from a taxi company raising concerns about a customer in the early hours of Wednesday morning.
They had initially been called to reports of a man with a gun robbing a taxi driver, Hertfordshire Police said.
When they arrived at the scene, they chased a suspect who turned on them - stabbing Finn in his head and chest and the officer in his hand.
A 16-year-old from Lewisham, south London was arrested on suspicion of GBH, conspiracy to rob, possession of a firearm and possession of a bladed article.
The dog was taken to a vet for emergency treatment, while his handler went to hospital.
According to the Twitter page for the combined dog units for Bedfordshire, Cambridgeshire and Hertfordshire police, Finn came out of surgery after four hours.
One post read: "The operation appears to have been a success & he'll now be closely monitored."
The suspect remains in custody.