A World War I Reference

Although a German woodsman called up in 1914 never returned, his widow claimed that:

"'...somehow she got a little money together during the war - English sovereigns if you believe my mother's tale of what her mother told her! Given to her by a secret agent she sheltered while he was ill!'"
-SM Stirling, Shadows Of Falling Night (New York, 2014), CHAPTER TWELVE, p. 238.

I sense a literary reference here. Which fictional secret agent of World War I was taken ill, sheltered by a German woman and paid her in sovereigns?

Somerset Maugham's Ashenden? John Buchan's Richard Hannay? Someone else?

Addendum: Having googled, I think that the secret agent is Hannay. See Greenmantle.

Addendum II: OK. The answer is given on p. 241.

(Our Muslim neighbors, having finished their Ramadan fast, have been chattering on the street and two young women from No. 40 have handed cakes in to us at No. 44. I am switching off the lap top earlier in the evenings in aid of a better night's sleep so this will probably be the last post for today.)