Denying any responsibility for this is: The Thinker
The author writes:
Of course by this point we all know the true identity of Captain Sims, but remember that Frank, Kelly, the Head Librarian and Don Hollister haven't seen what we have, so they're still all oblivious. That said though, Mrs Kilberton does know, but she's not telling for her own reasons. However, all this and more becomes irrelevant when every puts two and two together and realises just exactly what that porcelain duck in Mr Kilberton's garden shed really is...
Oh, and if you think that caps off the full extent of all the plot twists across this comic's story arcs, you obviously haven't been reading Postcard enough.