This story was produced in partnership with the Pulitzer Center.
CHISINAU, Moldova — Whenever Alena Mustiats' 5-year-old daughter hears sirens, the little girl comes running, backpack in hand.
"Sirena, sirena, sirena!" she yells to her mother, regardless of whether Mustiats, 40, is sleeping or showering. "Adventure, adventure."
The little girl doesn't understand that Russians have invaded her country. She doesn't understand that missiles or artillery shells threaten to rain down on Odesa, the strategic port city along Ukraine's southern Black Sea coast. She doesn't understand the mines the Ukrainian military has laid along the beaches where she used to play.
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She thinks the sirens are part of a game — unaware it's a deadly serious ruse her mother created to help her know when to grab her backpack and hurry seven minutes to the bomb shelter. The two practiced their "game" several times in Odesa before they fled to safety in Chisinau, the capital of neighboring Moldova.
"I tell her that maybe today we will hear fireworks, and we should listen carefully," Mustiats said of the times they hid in the shelter. "I tell her that we won't be able to see the fireworks in the sky, but we will always have to listen."
Although Odesa has been largely spared the kind of devastation seen farther east, residents look out each day to a flotilla of Russian warships menacing the coast. Authorities said those naval vessels shelled an apartment building on the outskirts of Odesa on Monday, heightening the tension.
For Odesa's residents and refugees, daily life is tethered to those air raid sirens: After Russian troops devastated Mariupol and attacked next-door Mykolaiv, this Black Sea city has become a safe haven for some, even amid the anguish and foreboding the sirens bring.
“It’s like a cold jump inside your heart every time they go off," Mustiats said.
"You go crazy listening to them," added Veronika Shyryaeva, another mother from Odesa, who fled to safety with two children.
Although the sirens are infuriating and frightening, many Ukrainians who fled to Moldova can't quit them, listening via an app that alerts them anytime authorities trigger a hometown alarm.
Mustiats and Shyryaeva reluctantly left Odesa, leaving the beaches and cafes and familiar faces for the safety of Moldova. Russia's invasion forced them — along with more than 3 million other Ukrainians — to flee to safety, leaving their husbands, brothers and sons of fighting age.
Shyryaeva, 46, is the fourth generation of her family to call Odesa home, and she mourns the loss of the life she knew. She brought two of her children to Moldova, but her eldest daughter insisted on remaining.
“It used to be easier there because until last weekend, Odesa had not been touched," she said. Monday, Russian airstrikes or artillery fire hit apartment blocks on the city's outskirts, causing a fire but no casualties, according to Odesa authorities. That attack startled many holdout residents into leaving.
Safely at a shelter in Chisinau, operated with the help of Catholic Relief Services and the Catholic Church-sponsored aid group Caritas Moldova, Mustiats and Shyryaeva are making new friends among their fellow refugees, including Olga Zadvornaya and her two daughters, who share a room with Shyryaeva and her kids.
Shyryaeva said her faith in God and her fellow Ukrainians sustains her, and she's eager to return as soon as she can: "I tell this to everybody, I want to go home. We want to build our future in our country. I am waiting every day for the phone call to come back home.”
That call may not come anytime soon. Ukrainians in Odesa say the city is eerily quiet now that at least half of the residents gone. Women and children are allowed to leave Ukraine, but fighting-age men must stay to help defend the country.
Construction worker Victor Romanenko said anti-aircraft weapons fired by Ukrainian forces sounded like fireworks when they went off Tuesday morning, and public transit has been curtailed. The once-popular beaches have been strewn with mines to deter or slow any Russian amphibious assault, and people do their best to help the needy or vulnerable who have not left, others said.
The U.S.-based aid group Team Humanity helped evacuate more than 2,000 people from Odesa and nearby Mykolaiv, cramming refugees on buses each night after delivering hot meals to the cities' defenders.
Romanenko said he is staying, despite the danger.
"My life is no more expensive than the life of young soldiers," he said via text. "If you are a woman, stay where you are now. If you are a man, come to Odesa to protect the city."
Kristina Logvinova risked a daytime visit Tuesday to Odesa from Chisinau to collect clothing and musical instruments her family abandoned during their hasty evacuation a few weeks ago. Driving through the city, she said the air raid sirens set her nerves on edge, especially after the peace of Moldova.
"I'm safe but not emotionally feeling very good," she texted. "It's hard to see what Russia is doing to my country and people."
Shyryaeva, the refugee in Chisinau, said Russian warships seemed to move close to shore, then back off with no pattern, creating even more uncertainty. In Moldova, she's free to focus on keeping her kids safe and helping others. She said that although the noise of anti-aircraft weapons firing near her house startled her at first, she welcomes the memory of that sound — because it was an audible signal that Odesa remained free.
“Mr. Putin wanted to split Ukrainians," she said. "But we are more united now.”