Migrants continue to take to the Med despite thousands of deaths. Credit:Raoul Kopacka There was no time to reflect. There was another medical scenario on another boat, one of 22 that had made it into international waters off the Libyan coast that day (eight of which were never found, never rescued). All nearby aid vessels were full to capacity. "It was just a quick check in this weird situation," says Pender, a 28-year-old Australian doctor who volunteered to work on one of those ships, and whose job it was to perform the first scan for medical emergencies on refugee boats they intercepted. "The baby looked OK."

Migrants on board a rescue boat. Credit:Raoul Kopacka But the moment "particularly sticks" with her, she says. "I think that's the pinnacle of the whole crisis. For me it just feels like every mother in the world has the right to meet their baby. It's just a horrible situation, the difference that exists." The Iuventa Ship of the German NGO Jugend Rettet is seized at Lampedusa harbour, Italy, on August 2. Credit:ANSA/AP The difference between us, writing and reading this story, and the people it is about. That mother, left dead on an African beach, as her child tried without knowing to reach sanctuary.

Pender doesn't want this to be a political story. She says it is a humanitarian story. It is about desperate people who need rescue, who (she has seen in the marks on their bodies, and has heard in the snatches of personal stories she gleaned while treating them) are fleeing abuse, torture and slavery. Rescued migrants are given thermal blankets. Credit:Theresa Leisgang She wants it to be about women like Virtue. That was the scariest moment of Pender's life. It was the worst-case scenario: a boat sinking even as they approached it. About 50 people were in the water. The surface of the sea was filmed with gasoline, which was inhaled by those in the water, wrecking their lungs, preventing them from getting enough oxygen. Dr Stefanie Pender undertook two rescue missions aboard the Sea-Watch. Credit:Raoul Kopacka

Pender was on the main boat as body after body was pulled from the water and "flopped" ominously onto the deck. They raced them into the ship's medical room. Many were barely breathing. "I didn't think she'd make it," Pender says of Virtue, who was in respiratory failure. Dr Stefanie Pender (third from left) with rescued children. Credit:Raoul Kopacka After six hours of oxygen and care, Virtue improved a little. She asked about her baby. She was six months pregnant. Pender found it hard to bring herself to check, but Virtue said she felt it moving. So Pender listened for a heartbeat. And heard it.

"It was the most beautiful sound in the whole Mediterranean." Later that night Pender had to identify another pregnant woman, who had been on the same boat as Virtue, but didn't survive. "No-one knows her story." Pender doesn't want this to be a political story. But for the last three months she has been working in one of the most politicised patches of water on the planet. Though the numbers are slightly down on last year, still thousands of migrants are attempting the crossing from North Africa to Europe, and thousands are dying in the attempt.

On the latest United Nations data, there have been 2408 migrant deaths in the Mediterranean in 2017, with 116,692 arriving in Europe by sea. More than nine out of 10 arrived in Italy – and a third of those were rescued by aid organisations, whose boats patrol the "search and rescue zone" off the Libyan coast. As Italy takes more and more migrants it struggles to provide for, and its neighbours shut their borders and refuse to take a share, there has been an increasing pushback. Italy has tried to impose a code of conduct on aid boats that would restrict their operations, with some Italian prosecutors and politicians accusing NGOs of providing a taxi service for migrants – and by extension traffickers. Europe provided resources to encourage Libya to intercept boats on their way north. That's the macro story. Pender has seen it in action. She has stood terrified on a flimsy rubber speedboat as a Libyan gunship bore down on her, determined that she should not help the desperate people she was about to rescue. And last week she was interrogated by Italian police after the Iuventa, the ship she had been working on for her third rescue mission, was seized and then confiscated, accused of colluding with people smugglers.

In a Skype call from Malta, Pender is diplomatic and cautious. She tells me, as she told the police, that she saw nothing untoward or odd in the mission, and she was worried the seizure of the boat would prevent them saving lives. "It's just a distraction from the real issues ... the fact that people are dying almost daily in the Mediterranean," she says. "It's part of the toxic narrative and these attacks [the accusations that NGOs are collaborating with people smugglers] have already been refuted." She provides me with an account of Iuventa's seizure, co-written with a colleague, that makes it clear she suspects foul play. "Events of the past few days have forced us to question the integrity and priorities of European search and rescue authorities," they wrote. They outlined a complicated series of events involving the transfer of rescued migrants, a strangely fruitless search and rescue mission, and then the impounding of the ship operated by the German charity Jugend Rettet (literally 'youth rescues'). The MRCC, the official centre in Rome that co-ordinates rescues in the Mediterranean, "either dangerously mismanaged the rescue operation or had other motivations for their decisions", they wrote.

None of the three incidents being investigated took place during Pender's mission. Trapani prosecutor Ambrogio Cartosio, who briefed media on the allegations about Iuventa, said his "personal conviction" was that the aid group's motive was humanitarian, and it "would be fantasy to say there was a co-ordinated plan between the NGOs and the Libyan traffickers". Pender studied medicine in Melbourne and worked there for a year, then the last two years in Darwin. She hasn't specialised yet, but a lot of her work in Darwin is in women's health. She was on a course in Europe earlier this year when a friend of a friend asked if she was interested in working on a Mediterranean rescue boat. The German group Sea-Watch needed a doctor at the last minute. "And the next week I was on a boat," Pender says, laughing at the memory of how abrupt it was. She had little idea what she was getting into – the first of her three rescue missions to date.

"I don't think I could have imagined the situation," she says. "It's very much more than I was expecting, and completely overwhelming." First there's a point on the horizon, then you start making out bodies, then you start making out faces. Pender's job was to hop into a RHIB, a small speedboat, to make first contact with the refugee boats. It's a delicate time. "They're all extremely overcrowded," she says. "The worst-case scenario is when the boat collapses or when people are in the water or jump into the water." "There's about 200 people that are extremely desperate and in fear that their boat will go under."

Many are angry. Pender doesn't know what they're told at the Libyan end, but they were clearly not aware of the situation they were going into. She gets the impression some were told Italy was four hours away by boat. "So the realisation that they are just stuck in the middle of the ocean and that we found them with binoculars wasn't the understanding that they had. "We approach the boat and start by just waving, you try and keep the situation very, very calm because it's so tense that it can become very panicked quickly. You explain that we're there to help and we're going to give everyone life jackets. "We circle around and that's when I'm trying to make an assessment and see inside the boat if there is anyone looking really unwell." It varies, but in many boats there are very sick – even dead – people. She has seen extreme dehydration, people who have been exposed to the sun for days or sitting in a corrosive, poisonous mixture of salt water, engine fuel and human waste. Some had fresh wounds, from whatever happened to them before (or when) they boarded the boat.

She's had to deal with very sick or unconscious people, sometimes performing CPR in the speedboat. Back on the main ship she is usually flat out treating the sick, handing out food and water. But she has heard stories from women of the slave camps in Libya, of "being sexually abused almost nightly, a lot of violence and being forced to work for little or no money or just a bit of food". "I just had so many medical things to do that I didn't really get to delve into the stories, but from what I can understand Libya is just hell on earth." She has seen relief and a lot of joy in those rescued. "Far above all, I am deeply touched and inspired by the beautiful people I met – their stories, strength, perseverance and remarkable ability against their horror to manage a smile and keep hope," she wrote home in a letter to her brother, who was helping raise money for Sea-Watch. But some were beyond relief: children so traumatised they no longer cried.