New set pictures of Doctor Who have been released, and they’re teasing another Bad Wolf mystery. Doctor Who fans are already excited about the return of David Tennant in the 60th anniversary special and eager to find out what is happening to the Doctor to cause the degeneration. Tennant is not the only returning star, with Catherine Tate returning as Donna Noble and showrunner and writer Russell T Davies back at the helm. The 60th anniversary teases a wild journey into the Doctor’s past and this could continue into the new season when Ncuti Gatwa takes over as the fifteenth Doctor.

Fans have spotted call-backs to Doctor Who in new set photos. Doctor Who has been spotted filming in Bristol and shows the return of Minto Road (via Twitter). Minto Road was first mentioned by Mickey in the season 1 finale, “The Parting of Ways” when he asked Jackie, “Have you tried that new pizza place on Minto Road?”. Other nods to Davies’ first season include a poster advertising Henricks, where Rose Tyler worked, and promotional material for Albion, a political party that shares a name with the hospital featured in season 1, episodes 4 and 9, “Aliens of London” and “The Empty Child” (via Radio Times).

Related: Doctor Who's New Story Is Everything RTD's Season 14 Needs To Be

Doctor Who's RTD References Could Be Repeating Bad Wolf

Doctor Who

Doctor Who’s references to RTD’s first season could be repeating his Bad Wolf storyline, which spanned a long period of time with quick references dotted throughout. Small facets of the Doctor’s past appearing in his present on walls, on the TV, and on road signs echoes Bad Wolf’s development which could even indicate a return of Bad Wolf herself. Plus, with it being RTD’s first season back at Doctor Who it makes sense that he would be mirroring his iconic mystery style from his very first Doctor Who season as a way to bring Bad Wolf back, especially with Tennant’s involvement in the 60th anniversary special.

Bad Wolf returning is a possibility, however, RTD using these references to create a long-running mystery is not confined to Bad Wolf’s story. RTD used this style with Saxon, or the Master, during Tennant’s run as the Doctor and let all the small hints lead up to a big reveal. RTD loves the long-running mystery, so it is not surprising that he would begin his Doctor Who using the same style he is so recognizable for, as it has worked so well for him in the past, and it puts his stamp back on Doctor Who.

Doctor Who's Callbacks Can Explain Tennant's Return

David Tennant regenerates into new Doctor in Doctor Who

Davies including these callbacks can explain Tenant’s return as the Doctor, and makes the callbacks seem more than just fun Easter eggs. From an in-universe perspective, something could be behind all these illusions of the past and the links to the early Doctor Who season s the idea that the 60th anniversary special will be following a problem in the Doctor’s timeline. The callbacks are not from Tennant’s era, so these mixed with Tennant’s return could mean something is throwing these allusions to the past at the Doctor to cause him confusion.

These callbacks could also the Doctor Who theory that the Toymaker has returned to finally defeat the Doctor and is using a Doctor clone to do so. The Toymaker, suspected to be played by Neil Patrick Harris, is almost godlike and could easily bring back references from the Doctor’s timeline to cause chaos. One classic Doctor Who strip saw the Toymaker create a fake Doctor to fight the real Doctor, so it would make sense the Toymaker could do this and use tiny moments from the Doctor’s past to confuse him even more.

Related: RTD's Writer Criticism Reveals A Lot About Doctor Who's Future

Doctor Who's References Could Just Be Easter Eggs

Doctor who 60th anniversary special

Alternatively, these callbacks could be nothing more than fun references for long-term fans to spot. The use of Minto road, Henriks, and Albion are such tiny details, and were not important to the plot line of season 1, that RTD could just be including homages to his Doctor Who revival for eagle-eyed fans. It does sound like something Davies would do as a small nod to the Whovians, especially as the Doctor Who universe is expanding, and more lore is being included, these references could just be fun ways to link the series together to emphasize the universe.

Plus, with the callbacks all being from RTD’s first season as showrunner on Doctor Who and the first season of the Doctor Who revival, it is a fun way for Russell T Davies to mark his return as showrunner. The reference being from his previous stint as showrunner does lean more towards them being harmless fun and a physical representation of his return on the show, especially with the references' lack of significance when they first appeared. However, it would not be surprising with RTD’s reputation that the callbacks mean a lot more than they first appear for the next season of Doctor Who.

More: The BBC Didn't Know Doctor Who's 2005 Relaunch Would Be A Success