This article identifies and tests a novel diagnostic for clause structure in West Circassian, a polysynthetic language with ergative alignment. The diagnostic concerns an unusual construction involving multiple wh -agreement in relative clauses. I argue that wh -agreement morphology uniformly tracks agreement with a wh -trace, and sentences with more than one instance of wh -agreement are surface manifestations of a parasitic gap dependency. Once multiple wh -agreement is understood in this theoretically familiar light, it can be used as a powerful tool for diagnosing asymmetries between various constituents in the West Circassian clause. By appealing to well-known constraints on parasitic gap licensing, the article demonstrates that the absolutive DP raises to a position c-commanding other clausemate DPs, and applied objects may undergo optional scrambling to a position above the ergative agent.