One day, while you're sitting quietly at home, the front door bell rings.
When you open it, two official-looking men step in.
''Security Services,'' they say, as they push their way past you.
They immediately go to your living room and begin looking for material: photographs, personal letters, documents on your computer.
''What are you doing?'' you protest.
''Have you got a warrant? Do you have reason to think I've done something wrong?''
''No,'' they say, ''but we don't like the look of you and we'd like to see what you've been up to.''
It sounds horrible, doesn't it?
Surely it would only happen in a totalitarian state, like Soviet Russia or East Germany.
But there is a good chance our New Zealand security services are already doing this.
Or if they are not doing it yet, they will be doing it soon. The only difference is that you will never see the men and you won't know they've been spying on you.
The data may have been intercepted with the co-operation of your internet service provider (such as Telecom or Slingshot), who are obliged to provide spy agencies with direct access to it.
Or it may have been collected in a vast new data centre in Utah and requested from our allies by an increasingly intrusive Government possessed of surveillance powers the KGB could only dream of.
Is it happening already?
It is difficult to know. But Americans have recently discovered that in their country it is.
According to reports published last week in the Washington Post, the National Security Agency (NSA) has been collecting the details of millions of Americans' telephone calls. More frightening still, they apparently have access to the servers of Microsoft, Apple, Facebook and Google.
They can rifle through your emails at will and observe what you're searching for on Google while your fingers are still on the keyboard.
Keep in mind, too, that new legislation permits the indefinite military detention, without trial, of anyone merely suspected of supporting a terrorist organisation. Americans had better be careful what they search for.
As one former NSA agent put it, his thumb and forefinger close together, ''we are, like, this far from a turnkey totalitarian state''.
How does this affect us?
There are two facts about these American revelations that ought to give us pause for thought. The first is that the NSA claims to be collecting only data that relates to non-US citizens.
That, of course, includes most of us, since almost all our online data at some point passes through servers in the United States. If, for example, you use Google Docs, your information is almost certainly stored in the US and therefore accessible to American spy agencies.
The second is that the British equivalent of our GCSB, the GCHQ, has already been receiving information from the American spy programme. So it is likely our Government has been doing the same.
It is true that they hardly need the Americans. Our own laws allow not just the GCSB but any government department to gain access to our telecommunications network to spy on us.
The Government can, if it chooses, give IRD or Work and Income access to your emails or documents stored online. But our Government can deny they are spying on us, if someone else is doing it for them.
''But,'' we are told, ''they're only after the bad guys. The innocent have nothing to fear.''
Well, perhaps, although it depends on who decides who the bad guys are.
If I write an email expressing opposition to the Trans-Pacific Partnership (TPP), being negotiated in secret with the US and seven other countries, will I be considered a threat to New Zealand's ''national security or economic wellbeing''?
Note the ''economic wellbeing'' clause. If a government considers the selling of state assets to be essential to New Zealand's economic wellbeing, would this allow it to monitor anyone who publicly disagrees?
The decision will never be openly challenged in court; indeed, you may never know about it.
In any case, you don't need to have done anything wrong.
As Senator Dianne Feinstein, chairwoman of the US Senate Intelligence Committee, said recently, this information is needed ''in case someone might become a terrorist in the future''.
Well, I guess I might look like a likely candidate, at least to some over-excitable spy. As a religious studies lecturer I have taught courses on Islam. One of these dealt with Islamic revivalist (''fundamentalist'') movements.
Today, of course, many such movements have websites and I considered it part of my job to see what they have to say. Will my Google search records now be used against me?
What about you?
You may not have been looking for radical Muslim websites. But do you want any government agency to be able to discover what you have searched for on the web?
Think for a moment.
What could be done with that information?The United States has a written constitution.
The Fourth Amendment guarantees ''the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures''.
So the legislation that permits the American spy agencies to act in this way is almost certainly unconstitutional, although it may never be overturned.
Section 21 of our Bill of Rights offers a similar guarantee, but what protection does it offer when we do not know what our government agencies have been up to?
This has nothing to do with being left-wing or right-wing, a supporter of the present Government or of an opposition party.
Basic liberties affect us all. The point is that those official-looking men may already be inside the house. Let's find out.
If they are, it's surely time to show them the door.
