Spike began as one of Luna Torquill's countless rose goblins. It acts as a messenger and can do small, innate magics like don't-look-here spells. It is quite vocal, though only Luna can understand its catlike chirps and purrs. It is incredibly loyal and endearing, and it enjoys car rides.
Caring for it only requires sunlight, water, and fertilizer.
When Toby meets it, Spike is about the size of a small cat; over the years it grows to the size of a small dog and is promised to grow even larger in time. Toby is delighted.
In the Series
Spike delivered to Toby the key to Evening Winterrose's knowe. Later, Luna instructs it to show Toby to the Luidaeg for help. It continues to follow Toby around until she absently gives it a name, and then becomes loyal to her. Toby's cats are wary of it at first, but soon enough they become comfortable companions.
Spike sticks closely to Toby during her other adventures, and she more or less lets it do what it wishes. Notably, it comes with Quentin to help Toby escape Blind Michael's realm. When Acacia sees Spike, she realizes that Toby knows Luna.
Although the Luidaeg banishes Cagney and Lacey from the room when she needs to speak privately with Toby, she recognizes Spike's loyalty to its new mistress and allows it to stay.
Spike allows Simon Torquill to stroke it when he comes to Toby's house and seems content to curl up on his lap.
Spike insists on traveling with Toby to the Kingdom of Silences, where he happily chatters with Ceres's rose goblins.
Spike accompanies Toby, May, and Quentin to Shadowed Hills and later assists them while they are on the Rose Road opened by Luna. It becomes separated from them but turns up again at home.