(Found) Early 2000's YA about a boy saving worlds on verge of momentous decision through a portal

[HalcyonicHermes]

The boy went through a portal type thing in a rundown subway or something similar. He could be transported to these worlds that were on the verge of chaos or being saved depending on a certain decision or action that was about to happen. I dont remember the antagonist(s?) but I think it revolved around the 3 earths, one set in the early 1900s, one set in current times, and another set in the distant future. The other worlds were all alien. The kid had some companion/mentor too but I dont know what/who they were. I think there were 7 worlds total but that could be wrong.

 

[psychotick]

Hi,

Could the tv series have been Voyagers?

Cheers, Greg.

 

[HalcyonicHermes]

Nah, it was a YA book series from the early 2000s.

 

[HalcyonicHermes]

Hi,

Could the tv series have been Voyagers?

Cheers, Greg.

Nah, it was a YA book series from the early 2000s.

 

[tachyon]

Did some searching, and it seems like the Pendragon Series by D. J. MacHale may fit the description.
First book "The Merchant of Death"

 

[HalcyonicHermes]

Did some searching, and it seems like the Pendragon Series by D. J. MacHale may fit the description.
First book "The Merchant of Death"

YES. THANK YOU.