Slow query spikes CPU

SELECT ah.[RSSAppHistoryKey]
,ah.[RSSAppKey]
,ah.[RSSPartyKey]
,[RSSAppType]
,[RSSAppStatus]
,[CreateBy]
,[CreateDt]
,[UpdateBy]
,[UpdateDt]
,[ActiveFlag]
,[RSSSourceSystem]
,[RSSSourceSystemRefKey]
,[RSSClonedFromAppKey]
,[RSSInitiatorGroup]
,[RSSHardstopReason]
,[RSSSupportFBO]
,[PartyUnregulated]
,[FundsFromUSCo]
,[AssignedTo]
,[RSSStatusExplanation]
,[SiteInspection]
,[SiteInspectionUpdateDt]
,[RSSEDDOutcome]
,[RSSEDDComments]
,ah.[RSSFunctionalGroup]
,[RoleOwnerCreateDt]
,[RoleOwnerProcessID]
,[RoleOwnerStatus]
,[RoleJointCreateDt]
,[RoleJointProcessID]
,[RoleJointStatus]
,[RoleAuthCreateDt]
,[RoleAuthProcessID]
,[RoleAuthStatus]
,[RolePoACreateDt]
,[RolePoAProcessID]
,[RolePoAStatus]
,[RoleBenOCreateDt]
,[RoleBenOProcessID]
,[RoleBenOStatus]
,[RoleBeneCreateDt]
,[RoleBeneProcessID]
,[RoleBeneStatus]
,[RoleGuarCreateDt]
,[RoleGuarProcessID]
,[RoleGuarStatus]
,[RSSCompleteCDD]
,[RSSCompletePEA]
,[RSSCompleteAD]
,[RoleOwnerUpdateBy]
,[RoleOwnerUpdateDt]
,[RoleJointUpdateBy]
,[RoleJointUpdateDt]
,[RoleAuthUpdateBy]
,[RoleAuthUpdateDt]
,[RolePoAUpdateBy]
,[RolePoAUpdateDt]
,[RoleBenOUpdateBy]
,[RoleBenOUpdateDt]
,[RoleBeneUpdateBy]
,[RoleBeneUpdateDt]
,[RoleGuarUpdateBy]
,[RoleGuarUpdateDt]
FROM [dbo].[RSSAppHistory] ah
INNER JOIN (
SELECT RSSFunctionalGroup, RSSPartyKey, MaxKey = MAX(RSSAppHistoryKey)
FROM [dbo].[RSSAppHistory]
WHERE ISNULL(ActiveFlag, ") = "
GROUP BY RSSFunctionalGroup, RSSPartyKey
) mk
ON ah.RSSAppHistoryKey = mk.MaxKey