You may remember Jack Finch from such comics as Bad Machinery. He has a long track record with Shelley’s sister Erin (and her antagonistic relationship with the mystery kids), but his run-ins with Shelley have probably been limited. I think his fellow child mysterion Lottie would no doubt have filled him (and everyone else) in on her mentor Shelley, doubtless at length. I thought maybe they had appeared on panel together but Linton was the recipient of the patronising hair ruffle back in this comic from a long time ago.