He possibly triggered the chain of events which led up to Covent Garden riot (among other things), by biting Brandon Coopertown on the nose. This brush with magic (possession by 'Mr Punch'?) seems to have given him the ability to detect magic and he will react to it, usually by barking. This has allowed development of a rough scale for measuring vestigia, where one 'yap' is enough vestigia to be apparent when not being looked for. The standard background of a central London pub is 0.2 yaps (or 200 milliyaps). Whilst the scale is primitive, further experimentation (Toby in a box with various materials) showed that plastic retained vestigia almost as well as stone.
Using his 'doggy supernatural senses' he tracked the murderers route from the site of the death of William Skirmish to the bus stop used on the journey home. Toby is loyal, and protected Peter when Molly briefly became unstable after performing haemomancy.
Toby accompanied Peter and Lesley when they were undercover at Skygarden, being a good excuse for walking out and about. He has some homing instinct, returning to the Folly after Skygarden was demolished.
Toby has assisted in tracking some supernatural creatures, a 'green man' in the first kidnap of Anna Yakunina. His ghost-hunting abilities were good enough to spot the train that the ghost of Alice Bowman was on, though he was scared of her, and ran off pursued by the ghost girl.