Purpose: This paper aims to answer report how mentors who onboard newcomers to a high-stress social work organization can learn about their onboarding practice by treating onboarding as a wicked problem that escapes definitive formulation and final solutions. Design/methodology/approach: The authors follow an action research approach with three iterations of learning about onboarding with mentors in a Danish social work organization struggling with an employee turnover exceeding 30%. Findings: The authors unfold the authors' emerging sensitivity to wickedity over the iterations of learning about onboarding with the mentors. As the authors foreground the wickedity of the authors onboarding in the last iteration, three lessons learned could be derived: it warrants the mentors' continuous inquiry; opens inquiry into the ambivalence of mentoring; and convenes responsibility for inquiry to a community of mentors. Research limitations/implications: This study of problematic onboarding to high-stress social work shows the value of fore-grounding wickedity instead of hiding it with a positive framing. This wickedity rests on situated grounding and is only transferrable to other organizations with the utmost caution. Practical implications: High-stress social work organizations without the capacity to systematically sustain best practices for onboarding may, instead, increase attention to the wickedity of onboarding as a motivation for continuous inquiry by a broader community of mentors. Originality/value: To the best of the authors' knowledge, this paper is the first to present an action research study of problem wickedity to motivate mentors' inquiry into onboarding newcomers to high-stress social work.