What secret does Standard keep from helmstone?

In the context of "The Secret of Helmstone," Standard keeps the truth about the ancient artifact hidden from Helmstone, fearing that its power could lead to disastrous consequences if misused. This secret creates tension between the characters, as Helmstone is unaware of the potential dangers and the true significance of their quest. Standard’s decision to withhold this information is driven by a desire to protect both Helmstone and the artifact from falling into the wrong hands.