Answer:
The scenario described appears to pose several potential contraventions of employment law, including:
Lack of written contract: Thomas has not received a written contract of employment, which is required by law in many jurisdictions.
Discrimination: Alex's actions, including refusing to include Thomas in social events and ultimately terminating his employment because of his HIV status, appear to constitute discrimination on the basis of a protected characteristic (in this case, disability).
Unlawful deduction of wages: Alex's threat to deduct pay from Thomas' wages for his absence due to medical treatment may be a violation of employment law, as Thomas had a valid reason for the absence.
Failure to provide training: Thomas has not received any training for his job, which may be a violation of employment law in some jurisdictions.
Unpaid overtime: Alex requiring employees to work beyond their contracted hours without pay is likely a violation of employment law.
Thomas should seek legal advice and consider filing a complaint or claim against the law firm for the potential contraventions of employment law described above.