It is still not clear exactly what happened.
But a young woman is dead; the first female British soldier to be shot and killed in Afghanistan, the third killed in action since the long war began.
And a young Marine from 40 Commando has died beside her, the 435th British soldier to die in a war that no-one in the military will say they are winning.
The two were part of a patrol that left its base in Nahr-e Saraj, probably the most dangerous district of Afghanistan for British troops.
They were not with Afghan troops or police, says the Ministry of Defence, but even the Ministry is struggling to work out what happened next.
It says an Afghan man, believed to be a policeman but not wearing his uniform at the time, died with them. One report suggests the Afghan was washing in a river before prayers.
Someone, perhaps mistaking him for an insurgent, opened fire. "We do not know what initiated the exchange of fire," says an MOD statement, "the situation remains unclear." Helmand's Police Chief is quoted as saying it is all, "a tragic mistake".
The Taliban, as they so often do, have tried to take credit for what happened, saying an Afghan in uniform opened up on the British patrol.
An Afghan police spokesman suggested two British patrols may have begun firing at each other.
The truth, for now, is lost in the fog of war.
British officers will have spoken to other troops from the patrol today but some are said to have been wounded themselves.
A few things are clear.
After eleven years of war - the longest in American history - six of them involving thousands of British troops at war in Helmand - longer than the struggle against the Nazis in World War Two - British men and women are still being blown up and shot dead.
The Afghan war continues to claim the lives of hundreds of soldiers and thousands of Afghan civilians every year. But there is no sign the government or the soldiers are making real headway against a determined Taliban enemy.
There is real nervousness now about allied soldiers and their Afghan counterparts patrolling together. Many joint operations have simply stopped. Two US soldiers have just been killed by a man in Afghan Police uniform.
The 25 year old female medic and many other young men and women in uniform continue to pay the price for a failing political strategy to change Afghanistan.
Forty-two-years ago a young soldier, later Presidential candidate, John Kerry, put a question to a Congressional hearing on Vietnam:
"How do you ask a man to be the last man to die for a mistake?"
Whether or not you judge the Afghan war to have been a mistake at the time, or more recently, or not at all, it is a question many in government would do well to keep asking themselves.