"My hands were shaking when trying to find the phone number for Tiritiri on my phone," Ms Sureda said.
It was Monday, February 12 - Waitangi Day was being observed, and the last ferry had left the island at 3.30pm. The next one was on the following Wednesday, and Mr Mold was without access to a boat.
"The lady was really distressed - she said surely I could get it to her somehow," he said.
After finding the passport, the ranger - who had worked less than a month in the island - dashed down to the nearest bay to see if there was anyone around.
"I noticed there were some yachts about 300m away, so I paddled out to see if any of them were going back to the city - but they were all sailing boats and none of them would have been able to get there in time."
Then he spotted a family fishing from a fibreglass speed boat. He paddled over and found they were willing to ferry the passport to Gulf Harbour.
Mr Mold then raced back to shore, jumped online and found an airport shuttle company in the area.
After explaining the situation to a staff member, a van was sent to pick the passport up from the wharf.
It was delivered for $160 to a very relieved Ms Sureda at Auckland Airport just 10 minutes before check-in was due to close at 9pm.
She messaged Mr Mold to say thank you:
"I'm at the gate waiting to board. I just thought I could not leave without sending you a few words to say that I'm fine and will be able to go back home. Many, many thanks. I will never be able to give you the favour back, but I am immensely thankful," she wrote.
"I was actually pretty rapt when I got the message from her - I felt pretty chuffed," Mr Mold said.
Back in Europe, Ms Sureda said without his help, she would have lost her ticket.
"I would have had to buy a new one, which meant of course a lot of money, time and more anxiety.
"That evening my partner would have had to fly home on his own and I would have stayed in Auckland.
"I'm immensely grateful to Matthew."
Though she would not be able to return the favour personally, she said she would keep Mr Mold's reply to her message of thanks in mind: "If you ever get the chance, pay it forward to someone who needs it," he said.