Canon Background
https://awoiaf.westeros.org/index.php/Kem

In-Campaign
Kem was working for Bathue, clearing tables, sweeping, doing dishes and more when he was approached by Teddy, Darron, and Dolins of House Jasper. They explained that they needed a child to pretend to be Zane Thorne and if he could do this he would live in a castle. They also shared that if he did not like the castle he only needed to stay a few days and then he could slip away if he chose. It was recommended he speak little while pretending to be Zane. Kem agreed with little thought, surely a castle would be better than toiling in Flea Bottom!

It was a week or so later when Kem met his host Jon Lynderly. Lord Lynderly quickly uncovered the truth, that Kem was not Zane. To Kem’s relief Jon accepted him into his service regardless after the lords (Jon and Teddy) conferred and agreed to revised terms.