Given the time constraint and the need for specialized knowledge in financial markets, inviting a guest auditor from one of the organization's affiliates who has the required expertise is the most appropriate solution. This approach leverages existing internal resources with the necessary skills, which can be more efficient and cost-effective than hiring new staff or outsourcing the engagement. Additionally, it facilitates knowledge sharing and can help build internal audit capacity for future engagements.References:
* The Institute of Internal Auditors (IIA) - Standards for the Professional Practice of Internal Auditing, Standard 1210 - Proficiency