Walk round the port in Mytilini and you get an insight into the fraught relationship between Lesbos and its migrants.
On one side is the ferry terminal. Moored there at the moment is a Greek naval ship, designed to carry a mixture of tanks and troops, which is now being rapidly converted to transport people.
Watching that work being done are hundreds of migrants who have arrived on this island over the past few days and who are gradually being told to file aboard.
At some point, the ship will leave port and, almost certainly, taken them all to a detention centre on the Greek mainland.
If these people had arrived in Lesbos before 1 March, they would have been able to apply for asylum.
Yes, they would have ended up among the rubbish and filth of the official reception centre at Moria Camp, regarded by some as the worst refugee camp in the world - but they would also join a very long list of those applying for the right to stay in Europe.
And yet the Greek government has now changed the rules, stopping newly-arrived migrants from applying for asylum.
Instead, they are told to go on that military ship, and await a journey that is very likely to end in deportation.
Around the port you can find more naval vessels, from Greece, Italy, Portugal and Britain, which patrol these waters looking for refugees.
You see the ferry that runs between here and Turkey, often carrying people who have been denied asylum and are being return to the Turkish mainland.
But there is another boat to watch out for. The Mare Liberum is different yet represents something of huge significance. And Sky News spent a day on board.
For a start, the Mare Liberum is much smaller and older than the others in the harbour. It was built more than a century ago to go fishing.
It is made of wood, doesn't have any guns aboard, and is crewed by volunteers. It is also the point of hatred for some in this town.
The Mare Liberum is run by a volunteer organisation of the same name.
It cruises the channel between Lesbos and Turkey, not only looking for migrants but also scrutinising the work of the coastguard vessels that are here to offer assistance.
They claim to have seen dinghies being deliberately damaged, migrants being ignored while they struggle in the water and even boats being pushed back, out of Greek waters and back towards Turkey.
"We are there to watch them, to let them know that they are being watched, and to try to ensure they stick to international law," says Flo Strass, one of the crew members.
"It's impossible to know how they would behave if we were not here, but I think it would be different."
Strass was on board the boat less than a week ago, when it was moored in a Lesbos harbour.
Through the window, she could see a group of around 10 men approach, shouting at them and telling them to leave.
One of the men picked up a plastic container and poured petrol on to the wooden boat. Another banged on the window, yelling at them to leave harbour straightaway. They did.
There are plenty in Lesbos who enthusiastically support the work of this boat and its crew; residents who have themselves pulled migrants from the water, fed them and helped them.
But there are also those who feel that the huge wave of refugees coming to Lesbos has blighted their lives and changed their island. And they look at the Mare Liberum with resentment and anger.
When we left port, we did so in a hurry, and sailed off to the echo of jeers and abuse.
The crew - two men and three women - try to shrug it off, but their conversation is peppered with references to personal safety and contingency plans.
"It has never been like this before," says Phil Hahn, the captain.
"I have been doing this since 2015 and we have never faced these sorts of attacks."
It is not just the crew. A German photo journalist was attacked the other day; other aid workers have been intimidated. Some organisations have ceased their operations for fear of being attacked.
But the Mare Liberum seems to attract particular contempt. Perhaps because a boat is hard to disguise; perhaps because their work, out at sea, may seem to be helping people to make the journey, rather than just dealing with them when they have arrived.
Whatever the reason, they have become a focal point for the mood of discontent that has bubbled up on this island.
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As darkness starts to fall, we head back to the main harbour. Then the radio crackles into life - it is the port authority, saying that we cannot land. They are worried about protest and the threat of violence.
We wait, going nowhere for a while, then are told we can sail to another harbour, some two hours away. It is the same place where the group of men threatened to burn the boat, and the crew are reluctant.
The coastguard says it will guarantee the safety of the Sky News team, as we disembark, but nothing more.
Hahn is reluctant, but then concedes he has no alternative.
We motor towards the small port, the crew nervously looking out for anything untoward.
A few torches are trained upon us but nothing more. As we approach the jetty, two flashes of light from land are the agreed signal that we are safe to land.
We shake hands and jump off the boat. As I turn to look back, a coastguard officer is ushering us away. He tells us - loudly, impatiently - that we must leave "absolutely immediately" because otherwise "people will be here".
And by now the Mare Liberum is already sailing away, into the darkness.
A boat with a mission to help migrants, crewed by people who find themselves wondering where they can find safety.