Nurse having gone to tea with a friend out Ivalunk way they were playing 'devil in the dark' (259)
Now, what or where is Ivalunk? Google is no help, and no more is the OED. It's possible that Nesbit is humorously adopting a phonetic spelling to reflect the Nurse's London pronunciation, but even then I'm having trouble seeing what the word behind it is. 'Ivalunk' doesn't bear much resemblance to any London district I can think of.
Quite possibly I'm missing something very obvious here: feel free to put me out of my misery.