If an Agent Asks for a Favour

Prompt: Mycroft's minions alert him that John is stealthily entering MI6. John and James covered each other's asses once and have been friends ever since. Mycroft calls upon his brother Q to find out what they're up to. Bondlock crossover. Or, in which John is a BAMF and Mycroft likes to snoop (more than usual). Established Johnlock and eventual 00Q.