I teach a foreign language. Today I gave the written portion of my final exam. Students were asked to demonstrate some grammar skills in the target language. On one part of the test, one student gave an incorrect answer. Interestingly, this student gave a response that included material we haven't learned yet. To be specific, I asked students to conjugate a given verb in the future tense. This student conjugated the verb in the future PASSIVE, which we haven't learned yet. We haven't seen those forms yet even in passing. Based on the response, it seems obvious that this student must have accessed outside materials during the exam. The problem is that I didn't witness this, nor did witness any other suspicious behavior whatsoever from this or any other student in the class. This student does not have a history of cheating in my class. If you were in my position, what would you do? Let's go ahead and assume that the office will offer no disciplinary support.