"If you are in Hogwarts robes people will expect to know who you are…. if you're in Durmstrang robes - well, you can fade into the background…."
-- Delphi (CC2.4)
Scorpius Malfoy joins Albus Potter, who is with Delphi at the edge of the Forbidden Forest. Scorpius is suspicious of how well Albus and Delphi are getting on. Only Albus and Scorpius put on the robes from Durmstrang Institute as their disguise for going back to the First Task of the Triwizard Tournament, since Delphi feels she is too old to pass as a student (CC2.4).
Takes place early September 2020, probably during the second day after Albus and Scorpius escape from the Hogwarts Express and visit the St Oswald's Home
Scorpius is a bit suspicious of Delphi helping Albus, but it looks more like jealousy at this stage than an awareness of any wrongdoing (CC2.4).
From the Web
The theatre production opened in the West End of London at the Palace Theatre on 31 July 2016, with Esther Smith in the role of Delphi, Sam Clemmett as Albus Potter and Anthony Boyle as Scorpius Malfoy: Harry Potter and the Cursed Child, Parts One and Two